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Abstract

Physical habitat and hydromorphological processes are fundamental to river ecosystem functioning and essential for restoring rivers subjected to multiple stressors. Extensive loss and damage to river and floodplain habitats caused by centuries of industrial, agricultural and urban development are preventing many rivers from achieving good ecological status even in places where water quality has improved. Restoration of river health and long-term resilience cannot be achieved without the foundation of good hydromorphological condition. Despite this, assessment of river health continues to be dominated by water quality monitoring. This imbalance has been exacerbated by increased public anger about serious pollution incidents, prompting an upsurge in environmentalist democracy, often led by activists participating as ‘citizen scientists’ (CS) at a local scale. Compared to chemical and biological water quality monitoring, assessment of physical habitat and hydromorphological quality is difficult and complex and the legal basis for monitoring is weak, resulting in low public awareness. Moreover, hydromorphology is not widely promoted in education, and professional expertise is scarce. We consider how CS volunteers might contribute to survey and assessment of physical habitat, proposing credibility and fitness-for-purpose tests for this activity. Reliable field data collection and valid interpretation are dependent on purpose and end use, deployed through appropriate survey design, sampling strategy, training and quality control protocols. Flexibility in the level of technical competence required for different types of field survey, allows carefully focused CS participation, although substantial professional input is required to ensure scientific and legal credibility. We recognise the invaluable advocacy role that CS volunteers can provide in raising public awareness and habitat restoration work at local level. A technical forum to address methodological validity, harmonisation of sampling effort, compatibility of data platforms and uptake of results would provide scientific credibility and build trust between professional river scientists and volunteers necessary for the effective deployment and uptake of CS surveys. Managed interaction would help to maximise efforts to restore rivers to full health in the context of building resilience for humans and biota under future rapid environmental change.

Keywords

citizen science hydromorphology river restoration multiple stressors pollution control England Water Framework Directive field survey

Introduction

A keystone of UK environmental policies for >50 years has been science: ‘the evidence base’ has become a normative policy term. The major environmental regulator in England, the Environment Agency, (EA) prides itself on its ‘scientific leadership, advice, foresight and evidence needed to inform decisions’ (EA, 2023: 5). Political ambition for healthy, resilient rivers remains strong, (25-year Environment Plan: HM Government, 2018, 2023), although the multi-billion-pound costs and decadal timescales of remedying past damage nationwide are stark reminders of the effort required. However, there is widespread agreement that ‘the current system of water and environmental regulation no longer delivers the outcomes that society expects and needs’ (SSWAN, 2025). In response to recommendations made by the Independent Commission on the water sector (https://www.gov.uk/government/publications/independent-water-commission-review-of-the-water-sector), Government now plans to restructure the institutional arrangements for water pollution control in England, to improve industry regulation and environmental investment for river quality (https://www.gov.uk/government/speeches/government-initial-response-to-independent-water-commission-final-report/).

Professional-level application of science across a range of disciplines is fundamental for the sustainable management of rivers. Monitoring how rivers and their wildlife respond to multiple stressors such as land use and climatic change, pollution, water abstraction and engineering work is essential for maximising best environmental outcomes through regulatory, policy and operational decision-making (Jones et al., 2023). Systematic broadscale and project-related monitoring both require a high level of confidence in data collection and interpretation, involving substantial technical, financial and professional staff investment to ensure replication and validity of results. Equally important is provision of appropriate IT platforms for data analysis and harmonised sharing and use of outputs. Increasingly, monitoring information can be derived remotely (e.g. telemetry, drones, and map-based databases), but field survey remains indispensable for ground-truth validation and data interpretation. It is also, with suitable quality assurance and control, amenable to contributions from citizen science (CS) volunteers ranging from amateur enthusiasts to retired ex-professional river scientists. Maintaining the scientific and legal credibility of field survey methods for physical river habitat assessment, whilst identifying the potential for CS involvement is the major focus for this paper and we conclude with recommendations on how that might happen. An important context is provided by differences in the strong legal, technical and public profile attributes of water quality assessment and weaker ones associated physical habitat assessment and its core science of hydromorphology. The general principles of scientific and legal credibility apply beyond the UK but we use examples from England to illustrate specific points.

Context: Why does water quality dominate river health assessment?

Measuring river health in England and elsewhere is still dominated by chemical and biological water quality monitoring, despite organic and toxic pollution being only part of multiple stressors acting on a water body. Table 1 summarises the main scientific, legal and public awareness reasons why water quality assessment in England is based on a well-established, frequently sampled monitoring network used for classification and enforcement purposes (European Environment Agency, 2017), whilst there is no equivalent for physical habitat/hydromorphology. How can the authenticity, capability and influence of physical habitat/hydromophology assessment be increased and can CS contribute?

Table 1.

Main reasons for differences between water quality and physical habitat assessment of river health in England.

Factor	Chemical and biological water quality	Physical habitat and hydromorphology
Profile and context-setting [‘natural’ vs damaged]	High public profile. Newsworthy. ‘Instant’ (snapshot) assessment approach. Simple, easily recognised visual cues of pollution problems include discoloured water, fish kills, algal blooms.	Very low public profile. Subject matter heavily nuanced by aesthetics, scale, catchment history (especially land use) and upstream/offsite processes. ‘Nice’ landscape features easily misinterpreted as (semi) ‘natural’ state to untrained eye. Problems not immediately obvious and often require extensive searches.
Measurement [replication, validity]	Science base well researched. Industry-standard methods for chemical and biological water sample collection and laboratory analyses. High confidence in replication and validity of results.	Science base still not fully developed. Guidance for field survey covers wide variety of features, some of which are very difficult to distinguish without expert knowledge and experience of different river types. Sampling strategy and sample unit differ between methods. Subjective judgemental interpretation lowers confidence in replication and validity. Scale a major factor.
Metrics and classification	Classification based on calibrated, empirical data (e.g. pass/fail test for chemical determinands); biological indices using pollution-tolerance of indicator species.	Habitat quality and artificial modification indices based mainly on scoring systems derived by expert judgement. Limited calibration; no pass/fail criteria for class boundaries. Scale affects contextual and comparative analyses.
Legal framework	Strong regulatory framework (polluter pays principle) and well-respected river water quality classification reporting. Enforcement/prosecution straightforward when environmental standards (e.g. for sewage discharge) breached. WFD a key policy driver for broadscale water quality improvement (viz. good ecological status (GES)).	Weak regulatory framework outside statutory nature conservation sites. No ‘polluter pays’ principle in law (common law a poor substitute) so no pass/fail trigger for enforcement. Very few case studies of enforcement. WFD uses hydromorphology only as a supporting metric for achieving GES.
Investment outcomes [policy influence]	Large and widespread. Determines major mandatory pollution control infrastructure expenditure by water companies (£billions).	Small and localised. Biodiversity policy drives local and discretionary expenditure on river recovery (‘restoration’) effort outside protected river designations.
Political influence	Highly influential number of activists on social media. High profile cases of angling trusts taking private prosecutions against water companies.	Low public profile. Rivers Trusts still largely interested in river ‘restoration’ for fishery purposes. Unlikely to increase without a major campaign highlighting the need for action.
Deployment and CS involvement	Well-established, extensive national sampling network.	Very limited. Two national baseline surveys. Mainly ad hoc catchment and project appraisal survey effort. Very little CS involvement so far.
Deployment and CS involvement	Organised CS contribution (Riverfly) in addition to pollution hotline input.

Vitally, chemical and biological water quality assessment of condition (e.g. trends in chronic conditions and the thresholds between contamination and pollution) and compliance (for regulating pollution and other harms) use calibrated, industry-standard methods. Both objectives require careful consideration of the relationship between ‘weight of evidence’ and ‘burden of proof’ because monitoring results can result in legal process. Importantly, courts and judges can determine what counts as evidence and whether the case concerns performance or compliance (Dicks et al., 2014; White et al., 2022). There is no equivalent industry-standard process to support legal enforcement or challenge associated with physical habitat assessment, resulting in a weak EA response to illegal channel reshaping and dredging (O’Brien, 2024).

Despite the strong legal requirements for water quality monitoring, substantial funding cuts in government support for research and river management institutions from about 2010 has severely reduced river monitoring effort, incident response and legal enforcement activity by the EA (Box 1). The consequence is that ‘getting a complete overview of the health of our rivers (our italics) and the pollution affecting them is hampered by outdated, underfunded and inadequate monitoring regimes’ (HoCEASC, 2022: 5). Many environmental monitoring systems are considered not fit-for-purpose (OEP, 2024a), and half the 44 targets for environmental improvement have ‘data deficiencies or need additional indicators to monitor progress sufficiently’ (OEP, 2023). As a result, the Water Framework Directive (WFD) objective of 77% of waterbodies achieving ‘good ecological status’ by 2027 is more likely to be 21% (OEP, 2024b).

Box 1. Impacts of funding cuts on EA activity

• DEFRA grants to the Environment Agency have fallen by 56% compared with 2009–2010.

• Despite a rise in 2022/23 there remains a decline in real terms.

• Enforcement action has declined by 84% between 2012 and 2022.

• Prosecutions under the Agency’s regulatory powers fell from ca. 300 in 2012 to 20 in 2021.

• Of 4074 enforcement actions taken against companies during the same decade 59% did not result in a fine.

• In 2022, EA staff were instructed to ignore ‘low impact’ pollution incidents due to lack of capacity.

• Water pollution monitoring has been reduced to such an extent that few pollutants are monitored and reported in ways that allow preventative action to be taken.

• Context: The EA takes water samples for 42 different legislative contexts, >99,000 samples for 1800 determinands.

Sources: Colbert (2022); Browne (2024); https://environmentagencyblog.gov.uk/2025/03/06.

The current public and political focus on the ‘water quality crisis’ in England deflects attention away from the importance of multiple stressors affecting river health, including disruption to fluvial morphological processes and consequent degradation of physical habitat and impoverished river ecosystems. Gumiero et al. (2025: 20) wisely conclude that: ‘Pressures and measures with easily identifiable sources often appear more manageable than hydromorphological pressures, which frequently stem from legacy issues or multiple stressors’. It is not surprising that a recent global literature review of CS contributions to river science by Shao and Bishop (2025) reveals a dominant water quality role.

There have been no broadscale national surveys of river habitats in England (and Wales) since 2007–2008 (Seager et al., 2012), following the first, UK wide, baseline survey in 1994–97 (Raven et al., 1998a). Financial constraints in the EA undoubtedly have been a factor, but for pragmatic reasons the interval between these snapshot overview surveys will depend on the pattern and rate of change expected and granularity of sampling in relation to the very low (albeit statistically valid) proportion of river network covered (ca. 2% at 1:625000 scale). More intensive sampling in catchments to characterise specific reaches, detect impacts of planned development and assess the effects of local river restoration work represent another form of monitoring, commissioned as specific project work. Nevertheless, further national surveys will be required to assess long-term broadscale trends in river habitat quality and modification.

The lure of citizen science: A ‘cheap’ policy response to a crisis?

Public anger about the poor state and perceived neglect of rivers has generated considerable local action and therefore propelled CS to the forefront of the policy arena, with Government actively encouraging statutory organisations to collaborate closely with local communities and voluntary groups to help monitor river health (environmentagency-blog.gov.uk/2025/03/18/citizen-science-and-the-environment-agency/). During 2022–2025 the water industry regulator (OFWAT) has funded a national project (CaSTCo: the Catchment Systems Thinking Cooperative), rolling out prescriptions for CS engagement and involvement in all aspects of river quality (https://castco.org). However, under such socio-political conditions (including scarcity of professional expertise) Lave (2012a) has highlighted the very real dangers of ‘extra-mural knowledge production’. Substituting or depleting the critical mass of professional-level science (in any discipline) in favour of CS undermines the credibility of policy level decision-making, particularly in relation to the veracity of expert opinion. However, as a well-directed adjunct to improve local knowledge, CS has substantial potential benefit.

Britain has a long tradition of competent (including professional level) amateur, that is, unpaid, specialists (Allen, 1994; Freeman et al., 2007). As Mulgan (2020: 149) points out, ‘Citizen science has already transformed the everyday work of astronomy and zoology, counting and mapping stars and animals’. He also refers to the contribution of the Zoe ‘symptoms’ project during the COVID-19 pandemic in the UK (https://zoe.com/learn/category/covid/covid-symptoms). Many argue for the National Health Service to make greater use of ‘Patient-Generated Data’ (University of Manchester, 2022) but investigations in the field of human health reveal some of the caveats we make below about CS and river health (Cresswell et al., 2018; West et al., 2017).

The flagship CS participation in river monitoring is the Anglers’ Riverfly Monitoring Initiative, in which trained volunteers can reliably assess water quality conditions using the relative abundance of macroinvertebrate taxa indicative of pollution stress. Brooks et al. (2019) take care to relate the strength of Riverfly indices of pollution to those used in law, citing 5 case studies where their use has brought about water quality improvement without using prosecution. The availability of reasonably priced, accurate monitoring equipment for some water quality parameters, together with ‘real-time’ mobile phone data collection and transmission, has allowed an upsurge in CS engagement. The speed and flexibility of CS volunteers in responding to pollution incidents often beats that of the depleted ranks of the EA; Roger et al. (2024) express this as, ‘being place-based, making it more logistically feasible to capture episodic events’ (p. 1).

At least 10 UK eNGOs currently motivate volunteers to monitor the state of rivers, either in ‘blitz’ sessions, in pollution episodes or as a routine commitment. A major focus for CS involvement in rivers is the network of 65 Rivers Trusts in Britain and Ireland. Collins et al. (2023) highlight the Trusts’ use of citizen science to ‘engage and empower’. However, they admit that ‘the dominant approach within freshwater citizen science lies disproportionately at the lowest level of participation’. The transfer of professional scientific knowledge and capacity from statutory to voluntary sector seemed to represent an ideal opportunity for filling some of the WFD monitoring gaps at low cost (Newson, 2011). This was one element of a deliberate policy to increase involvement of CS across a wide range of disciplines (Fraisl et al., 2022). But there are substantial consequences resulting from a decline in professional field survey expertise and the validity of ‘expert opinion’. In addition, there are considerable costs for training, support and ongoing maintenance of CS participation: CS is certainly not a cheap credible alternative to professional science.

Semantic precautions in a diverse field of public environmental engagement

CS terminology is important because ‘citizen science’ covers a range of competency levels variously labelled with vague confusing terms such as ‘community science’, ‘vernacular/indigenous science’, ‘local knowledge’ or ‘nature noticing’ and defined by purpose and reasons for participation (e.g. Pocock et al. (2023), Guston (2023: 92), Gumiero et al. (2025: 11); Yeung et al. (2024)). The European Citizen Science Association (ECSA) sets out 10 principles for ‘fostering excellence’ in CS (Robinson et al., 2018), while the European Cooperation in Science and Technology (COST) network makes a granular analysis of many components of CS (‘The Science of Citizen Science’: Vohland et al., 2021). Most helpfully, CaSTCO has defined several categories of CS competency (https://www.castco.org/knowledge-categories/purpose/).

Mulgan (2020) sees CS as short-circuiting the existing barriers between science and democracy. ‘Most of the people involved in citizen science observe a strong ethos, a belief in the redemptive power of science, particularly in relation to observation and interpretation’ (p. 150). In this way, ‘science can become a shared activity, something integral to democracy and citizenship’. CS can/should promote environmental activism and strong representation; both these purposes and the relevant socio-political processes (‘the mechanics of virtue’) are behind the failure of public participation in river basin planning under the WFD (Rimmert et al., 2020; Van der Heiden & ten Heuvelhof, 2012).

With the advent of a catchment-based approach and place-based solutions, for example, to create flood resilience (Newson and Lewin, 2024), the involvement of these various sources and acknowledgement of their appropriate role, strengths and weaknesses are important to resolve (Roger et al., 2024). It may well be that ‘the place’ is the best scale for integrating professional and CS contributions to survey and ‘monitoring’: clearly, sampling and data collection harmonisation, supported by compatible IT platforms will maximise use of CS survey information at the national scale.

The Rivers Trust (https://theriverstrust/news/citizen-science-10-ways-you-can-get-involved-in-the-fight-for-cleaner-rivers) publishes a guide to using CS ‘in the fight for cleaner rivers’. All feature water quality and wildlife, none assesses physical habitat; it is concerning that only one CaSTCo demonstrator catchment (https://castco.org) is deploying hydromorphological assessment – that of an estuary. More recently, Shuker et al. (2024) illustrate a CS level hydromorphological appraisal for local river restoration. A more formal strategic and management menu for CS involvement with freshwater issues is provided by Bishop et al. (2021), whilst the River Restoration Centre (RRC) has a comprehensive online resource guiding users to the features of all the available survey/assessment techniques, including physical habitat and hydromorphology (https://www.rrc.org/).

Generic guidance on the suitability, reliability and usefulness of CS involvement in a range of environmental and ecological monitoring programmes has been developed (e.g. Sutherland, 2022), and several reports (e.g. Pocock et al., 2014; Tweddle et al., 2012) set out standards and procedures, albeit without an agreed consensus on ‘rules’ that might define appropriate CS data quality. Indeed, concerns about the consequences of a headlong rush to embrace CS without proper scientific input to planning and deployment have begun to emerge (e.g. Bowler et al., 2024; Fraisl et al., 2022). Tweddle et al. (2012) arrest their readers with an opening section entitled, ‘Before you start. Is citizen science the best approach’? More recently, the EA has provided eight generic guidelines that temper unbridled enthusiasm with sensible precautionary tests in planning and deploying CS project work (environmentagency-blog.gov.uk/2025/03/18/citizen-science-and-the-environment-agency). The main challenge for well-targeted and properly managed CS is the capability to incorporate, (like ‘mainstream’ scientific research does currently), strategically significant data that provide incontrovertible evidence to detect problems and opportunities that support or change the direction of environmental policy, including managing rivers. As with all scientific endeavour, a rigorous approach is required to ‘weight of evidence’, within the peer group even before any legal aspects of ‘burden of proof’ are encountered (Gough, 2007); lawyers also use the term ‘evidential value’. Kucharski (2025) goes so far as to suggest that legal frameworks my provide the best ‘proof’ for all science results. This challenge is uniquely severe in the case of the quality of physical habitat, as incorporated in the WFD’s ‘hydromorphological quality’ category.

Principles for monitoring and assessment of physical habitat

Much of the damage done to rivers has been physical (Newson, 2022) and recovery requires restoration of morphological diversity, with associated benefits for habitat quantity and quality, together with resilience to climate change. Whilst there was protest at the damage (and practical guidance on how to rectify it) it was largely from academics and NGOs (Purseglove, 1988/2017; Lewis and Williams, 1984; Ward et al., 1994).

River science professionals (sensu Newson et al., 2023; Wohl et al., 2015), with very good reason, emphasise the special expertise required in the field of river hydromorphology despite the criticism that ‘a common mode of conducting citizen science is to have lay people act, in essence, as volunteer research labour on a project designed by elite scientists for their own goals’ Guston (2023: 94).

Professional survey and assessment of physical habitat quality of rivers in England developed from the late 1980s when annotated field maps identified features of conservation interest that needed to be retained during river engineering work (River Corridor Survey: NRA, 1992). In the mid-1990s, River Habitat Survey (RHS) was developed (Fox et al., 1998; Raven et al., 1998a), collecting RCS – type information in a systematic, pragmatic way to characterise and evaluate the diversity and modification of river habitats in Britain at a 500 m scale. It was designed to help meet the WFD (European Commission, 2000) requirement for assessing ‘hydromorphology’, a terminological amalgam describing the interaction of flow and channel form that is the basis of physical habitat (Newson and Large, 2006). The first ever state of environment report for river habitat quality in the UK was based on a stratified random sample of >4500 RHS sites surveyed during 1994–97 (Jeffers, 1998; Raven et al., 1998a).

The WFD elevated the importance of river habitat by including hydromorphology as a qualifying variable for assessing ecological status its core river health index. Hydromorphology both directly and indirectly impacts overall river ‘health’: directly via the ‘ecohydraulics’ (Maddock et al., 2013) created by flow-substrate interaction and indirectly through transporting/depositing coarse and fine sediments (and inter alia persistent pollutants), acting as part of the ‘multiple stressor’ dynamics. Describing and assessing this complicated and complex environment is difficult technically and the methodology is still evolving, not the least because research in geomorphology, hydrology and hydraulics operates separately in the academic world (Newson, 2002); efforts to bring an amalgamated ‘river science’ to education have been limited (Newson et al., 2023; Vaughan et al., 2009).

CS hydrology remains the poor relation of engagement and participation, partly because it has remained a sophisticated technical activity, vital enough to be in professional and institutional hands. However, Buytaert et al. (2014) point to the recent availability of ‘robust, cheap and low maintenance sensing equipment’ offering opportunities for citizen participation. These authors also stress the challenge to CS hydrologists to ensure ‘the generated data complement optimally other available knowledge’. Nardi et al. (2022) report on the work of the International Association of Hydrological Sciences to develop online resources to inform and train CS participants.

Damage to physical habitat is also widespread because of the control of river flow regimes for water supply, wastewater and flood protection (Petts, 1988). Flow-regulated rivers with large headwater reservoir impoundments are categorised under the WFD as ‘Heavily Modified Waterbodies’, with the management objective of achieving ‘Good Ecological Potential’: GEP (SNIFFER, 2006, 2012), the equivalent of mimicking natural flow as far as possible. Central to achieving GEP is an environmental flow regime (Acreman, 2016) for reservoir releases; flow characteristics form part of the ‘multiple stressors’ concept. Vezza et al. (2015) develop an Index of Habitat Stress Days, alongside an Index of Habitat Quantity to describe the impact of modified flows on the fish community. The nature of flow regimes means balancing the needs of river ecology, human interests, including flood protection, and the ability of reservoir valves to deliver. Because of the legal restrictions on reservoir operators to balance water stored in reservoirs with downstream flood risk, finding an ideal compromise for releases in flood-prone catchments can be difficult or impossible. Remedying the ‘hydro’ of hydromorphology is, therefore unsurprisingly, considered ‘too difficult’ to resolve. Hydrological science and data streams are also more difficult to access by citizen scientists than simple water quality; a potential exception is mapping hydraulic biotopes via ‘flow types’ (Newson and Newson, 2000) which forms part of RHS. Newson et al. (2002) combined field-mapped biotope frequency and diversity (near flow gauging stations) with flow exceedances and undermined the accepted Q₉₅ protected environmental flows below dams and hydropower plants. Biotope mapping is appropriate to both professional and CS surveys.

‘Natural’ river form and process: A template for repairing physical damage?

A river obviously damaged by organic or toxic pollution offers immediate recognisable cues for deviation from clean-water state, although there are subtle natural forms of contamination. However, assessing deviation from ‘natural’ physical habitat is far more complex and the subject of technical debate. Natural state is defined by EU directives in terms of ‘reference condition’ or, in ecosystem protection, ‘favourable condition’. Whilst Directives relating to water and nature differ in their general approach to reference conditions (Mainstone, 2016), the common understanding is an unimpacted (or nearly unimpacted) state, equates to natural river function.

Inevitably, compromises and trade-offs have to be made in trying to simplify or categorise a very complex subject matter. Problems arise if surveyors are asked to judge the ‘naturalness’ of a particular site without using a full array of supporting information and cues, leading to unverified and often erroneous conclusions. That is why for scientific credibility, most professional surveys are predominantly data- and not opinion-driven; interpretation and associated categorisation are part of data analysis, not field assessment. This gives rise to a stark difference between surveys that characterise the physical form and habitats of channels and floodplains, followed by decisions about ‘what’s been altered’ (e.g. RHS), or purpose-built surveys of modifications and their impact (e.g. MIMAS). This dichotomy also applies to judgemental-based CS surveys, highlighting the pivotal role of professional input to surveyor training and especially data interpretation purposes. The latter is particularly important when distinguishing between morphological features caused by human interventions and those responding dynamically to fluvial consequences of rapid climate change.

In England today, it is virtually impossible to identify a ‘pristine’ river of any size outside remote headwaters (Raven et al., 1998b). Sear (2023) suggests that we have forgotten what a natural river looks like, whilst Moss (2015) asserts that disturbance is so widespread that freshwater reference states are in fact ‘anthromes’, not biomes. In a token acknowledgement of the virtually universal anthrome, the European Committee for Standardisation began its work on hydromorphology standards (CEN, 2020; see also BSI, 2004) by advocating ‘near natural’, with zero tolerance of obstructions like weirs but, arbitrarily, up to 5% (by length) of channel modified by, for example, bank structures. ‘Artificial bed materials’ are, however, limited to <1% by CEN (Boon et al., 2010). Scientific debates and dilemmas concerning reference conditions are explored by Johnson (2001), Johns et al. (2013) and Newson (2022); techniques used to define them vary from expert opinion to mathematical modelling – all having strengths and weaknesses. Szalkiewicz et al. (2020) promote the incorporating of local ecological knowledge to define both ‘natural’ and ‘damage’ prior to restoration design.

Johnson et al. (2020) propose a category of ‘working streams’: most research geomorphologists favour process as the definitive natural element of rivers because forms are locally controlled by the boundary conditions to those processes (Newson, 2002). In trying to counter the problems of scale, dynamic processes and naturalness in one simple survey technique, Rinaldi et al. (2013) devised the Morphological Quality Index; relevant expertise is still required for making competent qualitative judgements of departure from reference condition.

Natural England’s Priority Habitat surveys, deployed by the Freshwater Biological Association using CS volunteers uses ordinal scales of disturbance (i.e. departures) in flow, morphology, biology and chemistry to provide a rapid qualitative evaluation of rivers for the specific purpose of targeting statutory protection or restoration, focusing on smaller headwater streams (https://priorityhabitats.org). Trained CS volunteers make informed subjective decisions on a five-fold scale as to the physical, hydrological, chemical and biological naturalness of a georeferenced survey section, triggering professional follow-up action where needed.

For habitat damage to be indexed, departure from ‘natural’ conditions across an array of river types needs to be calibrated by survey, assessment and data processing systems. Walker et al. (2002), use habitat quality and modification scores (HQA, HMS) from RHS at a catchment scale to guide restoration priorities. Sear et al. (2010) use professional, expert Fluvial Audit to yield greater site detail for restoration decision support.

Hydromorphological factors within the panoply of multiple stressors

Science and the law seek ‘truth’ and both disciplines have strict rubrics about pathways to reach it. Given the range of legal implications possible for hydromorphological assessment and monitoring, both CS and professional evidence must therefore be ‘fit-for-purpose’. That purpose needs to reflect the topic (within, say, river monitoring) and the levels of detail, certainty and accountability scientists consider necessary for producing evidence acceptable as proof. The issue has been carefully addressed by the US Environmental Protection Agency (1996) in guiding CS workforces such as that of the Chesapeake Monitoring Cooperative (2020). It is also a feature of the CaSTCo project, where five tiers of ‘seriousness’ for hydromorphological assessment techniques (five of nine of which are CS) are used to assist project planning (https://www.castco.org/knowledge-base/overview-physical-habitats/).

There have been few comprehensive and critical international reviews of operational hydromorphological survey and assessment systems. Berletti et al. (2015) come close to making useful critical judgement with a tabulation of ‘strengths and weaknesses’. Overview papers attempt to set out the principles of a good physical habitat or hydromorphology survey, including appropriate spatial scaling. Retrospective QA/performance indices are virtually never performed: only ‘successes’ get published, despite reporting failures being equally important to ensure (as in medical science) the best investment of effort and resources.

In addition to the paper by Belletti et al. (2015) there is the more recent and policy-related work by Papangelakis et al. (2023a,b). Both reviews highlight the lack of direct process assessment or variables directed at uncovering morphological process. Papangelakis et al. advocate the need for flexible systems that allow surveys to match more closely with local conditions, project aims and requirement for detail. This was also a theme of the REFORM project (Gurnell et al., 2016; Rinaldi et al., 2013) which led to CS-focused MoRPh (Shuker et al., 2017) in the UK. REFORM was an important influence on moving the WFD away from simplistic ‘refcond’ (Mosselman et al., 2024). Assessing the suitability of a particular method requires clarity about overall purpose so that a deployment plan contains the appropriate sampling strategy, quality control protocols and technical support needed to ensure validity and uptake of outputs. This applies to hydromorphology in particular because of the complex difficulties involved in trying to characterise and measure suitable parameters that relate to the scale and processes associated with the river continuum. To extend and develop the work of Berletti et al. and Papengelakis et al. (and as our contribution to the CaSTCo project) we accessed full technical details, uptake and deployment literature for 26 hydromorphology survey and assessment methodologies. Our purpose was to reveal characteristics that would help user individuals or institutions select a methodology ‘off the shelf’ or develop one of their own. Particular attention was paid to variables qualifying the field survey/assessment for CS deployment or as a basis for collaborative use with professionals. Recommendations were eventually cast according to fitness for purpose (See Table 3).

The pedigree of RHS gives the system ‘fitness’ and it has fulfilled its main purpose of assessing the physical state of rivers nationally and assisting assessment of compliance with the EU WFD. The RHS national surveys of 1994–7 and 2007–8 suggested 62% of sites were obviously modified or significantly modified (Environment Agency, 2010). Of the prominent modifications to channel form, bank resectioning (43%) and reinforcement (8%) showed little change, implying no statistically detectable overall deterioration or habitat recovery in a decade (Seager et al., 2012). Indeed, the most profound change was the increase in invasive non-native plant species, notably Himalayan balsam (Impatiens gladulifera). A CS version (https://www.therrc.co.uk/cRHS/cRHSManual) has been deployed in Wales, linking directly to the full RHS dataset.

The independent advisor to Government on the implementation of environmental law, including the ‘retained EU law’ (the Water Framework Directive, until 2027) and has recently reported on progress made in England (OEP, 2024b) and the Government has responded (Defra, 2024). Separately, the Environment Agency and Natural England have reported on ‘Indicator B3: State of the Water Environment’, a feature of the 25-year Environment Plan (Gov. UK; 2024). Both reports reveal the state of hydromorphology and the physical modification of waterbodies (proxy reporting scales for the WFD). Indicator B3 shows that 58% of rivers and canals have hydromorphology capable of supporting Good Ecological Status (the indicator target for WFD), compared with 76% for aquatic macroinvertebrates, 43% for fish and 45% for macrophytes and phytobenthos.

The Government response to the OEP report (Defra, 2024) refers to ‘the challenge of physical modification of water bodies’ (p. 6), which ‘in some cases over centuries, severely disrupts natural ecological process’. Despite this ‘physical modification of water bodies is the primary pressure preventing good status’. OEP concluded that the current monitoring programme is inadequate and argues that ‘this has resulted from EA budget cuts in this area’. The European Environment Agency (2024) shows that the UK is not alone in failure to reach GES on schedule and many of the pressures are shared. 51% of EU waters do not reach ‘good’ hydromorphological condition.

We have deliberately made frequent references to water quality issues, not only because of their current prominence in CS development in England (an international phenomenon – see Shao and Bishop, 2025), and the lessons for scientific integration already emerging (such as CaSTCo) but because damaged freshwater habitats should be considered the result of multiple stressors and optimal remedial action should reflect this.

The concept of multiple stressors has vital implications for the deployment of both professional and CS in river survey and assessment. It gains momentum from the work by Whelan et al. (2022) who claim that at least seven new stressors undermine the assertion that water quality continues to improve. Awareness of new risks such as microplastics (Dent, 2023; Woodward et al., 2021) and pharmaceuticals (Wilkinson et al., 2022) implies that CS contribution based on the simplest chemical and biological indicators can at best raise awareness because these new compounds require sophisticated analytical laboratory equipment. Likewise, to avoid erroneous conclusions, field survey data validity is fundamental for confirming hydromorphological stress at site, reach or catchment scale. This constrains CS involvement to those with an advanced level of training and competence such as that required for MoRPh and cRHS.

Despite better understanding of multiple stressors the biological response remains debatable. Analyses of aquatic macroinvertebrate data against environmental variables by Jones et al. (2023) reveal that temporal variability in stressors, such as dissolved oxygen, may be more important than average or point values. However, neither those analyses nor similar ones in other studies use the hydromorphological quality variables we advocate in this paper. Of those physical variables used by biologists, fine sediment pollution has dominated (reviewed by Jones et al., 2012). Jones et al. (2023) warn against the use of stressor-specific relationships but not including hydromorphic variables clearly affects this conclusion. Also using aquatic macroinvertebrate data, Qu et al. (2023) reveal no decline in diversity or sensitivity indices between 1989 and 2018 for 1515 sites in England, although improvements slowed after 2003 at some sites. Further analysis of macroinvertebrate data from urban streams (by Qu et al., 2025) illustrates consequences of multiple stressors, suggesting that, ‘the urban pollutant cocktail together with channel modification harm local native aquatic species and reduce biodiversity’ (p. 2), with Lapointe et al. (2022) emphasising the stress posed by stormwater runoff.

Natural, dynamic riverine ecosystems have inherent water purification properties such as hydraulic flow-related oxygenation and carbon sequestration by headwater and riparian wetlands (e.g. Everard, 2012); damaged physical habitats exacerbate the impacts of river pollution and low flows caused by drought or excessive water abstraction. Toxic heavy metals (e.g. zinc and copper) and persistent organic compounds (e.g. organophosphorus insecticides) can remain in river sediment for some time, creating a long-term pollution hazard that delays the recovery of affected biota (Langford et al., 2012). Recovery is also influenced by the proximity of unpolluted habitat refugia that act as recolonisation sources (e.g. Raven and George, 1988; Sedell et al., 1990).

Restoration and river system resilience: Longer-term opportunities for CS

Many of those activists who consider that involvement via citizen science in improving attention to, and remediation of, the poor state of rivers in England will also support river restoration; they are not alone. Currently 41% of water bodies are affected by physical modifications – more than pollution from rural areas and pollution from wastewater. The UK 25-year Environment Plan (HM Government, 2018, 2023) has undertaken to restore 4,000 km of river channel in England damaged by previous flood management interventions – essentially repairing physical habitat. Natural England, bound by the Habitats Directive, has commissioned plans for restoration action needed along 1,684 km of rivers qualifying as 22 Special Areas of Conservation, 16 of which have physical modifications (Natural England, 2015). However, the ideal of restored catchment-wide freshwater ecosystems via local physical restoration has rarely been validated by monitoring and can be largely driven by social or aesthetic designs.

Professional river science has confirmed that the primacy of physical damage in a field of multiple stressors (revealed by WFD reasons for failure) is real. Recovery will take substantial time and require physical and financial resources that are simply not available during fiscal stringency. Realistic integration of professional and citizen science effort is essential to optimise restoration ambitions: that means managing expectations to avoid disappointment. The field of ‘natural channel design’ and the involvement of non-professionals in physical river restoration is highly contested (Lave, 2012a; 2012b) and the ‘Rosgen Wars’ in the USA reveal the dangers and risks faced by ‘extra-mural knowledge’. The entry of extra-mural players becomes more likely given the shortage of professionals in the UK and the lack of specific physical habitat measures in current UK catchment management plans (Robins et al., 2025).

The concept of multiple stressors renders simple restoration of physical features in the river channel liable to disappointing outcomes (Palmer et al., 1997, 2010), who claim (1997: 291), ‘Many untested assumptions concerning the relationship between physical habitat structure and restoration ecology are being made in practical restoration efforts’. In part answer to the criticism, some research attempts to include the diversity of hydromorphology as a leitbild, for example, Gostner et al. (2012) use hydraulic variables; Dawson and Ashmore (2025) employ a more sophisticated analysis and indexation of form diversity. There are no recommendations for restoring the hyporheic zone (Buss et al., 2009) and even advocates of restoring connectivity between channel and emergent/floodplain sediments omit this critical aspect (e.g. McCabe et al., 2025). Worse news on restoration outcomes is presented by Theodoropoulos et al. (2020) who model six restoration structures at a range of four discharges for five biota/life stages. They conclude that physical restoration should be reserved for species of conservation importance at low, dry weather, flows.

The impacts of multiple stressors need to be identified as part of restoration design and post-project monitoring, and the inherent complexity is best handled by modelling. For England, Wilkes et al. (2024) use data for 188 macroinvertebrate taxa with data for abstraction, morphology, nitrates and phosphorous to draw up a restoration strategy, ‘the first national prioritisation’ together with climate change and socioeconomic change. This approach inevitably involves a catchment-based approach and provides a big CS opportunity to work with river science professionals. Even before funding cuts, England was short of such professionals: Newson (2002) (p. 376) ‘we have only a moderate proportion of the intellectual and financial resources needed to satisfy the clients for applied fluvial geomorphology within the short timescales available for providing ideal predictive, prescriptive and precautionary options for sustainable management of rivers’.

Will a coordinated partnership with suitably competent CS volunteers deliver more or better physical habitat survey and assessment? ‘More’ can include local monitoring of restoration (especially whether geomorphic complexity works (Dawson and Ashmore, 2025), extend official monitoring at a time of decline and lead to post-project appraisal becoming a condition of funded restoration projects. ‘Better’ could include ecohydraulic understanding through biotope mapping and a better evaluation of multiple stressors using the best survey assessment of each (e.g. Shuker et al., 2024). Clearly, both ‘more’ and ‘better’ will require substantial, planned and permitted work at the catchment scale, extending well into neglected headwaters (Robins et al., 2025) to determine the extent and location of pressures and impacts. Such a grand scheme of ‘biocomplexity across spatiotemporal scale from headwaters to large rivers’, through river ecosystem synthesis (RES) is advocated by Thorp et al. (2006); Vermaat et al. (2016) contrast project intensity with extent, with most restoration anchored at the reach scale.

This ‘anchoring at the reach scale’ is both the challenge and the experience of CS contributing to river restoration. It is in many ways the best suited, focusing on place. One example of such a joint venture is described by Shuker et al. (2024): trained CS volunteers carried out six pre- and post-project assessments using MoRPh. However, the work involved a river reach about 2 km long within a 43.5 km² catchment. MoRPh is specifically designed for CS but there are obvious dangers that local bespoke CS initiatives such as Westcountry Rivers Trust’s CSI (Citizen Science Information), which greatly oversimplify physical habitat assessment, will be scientifically invalid for comparative purposes beyond the limited geographical scope of deployment (https://www.wrt.org.uk/westcountry-csi/).

Further deployment of CS volunteers will come through their involvement in the construction of Natural Flood Management (NFM) including simpler, more biologically meaningful in-channel structures (Barrett et al., 2024). For working examples, see https://wyreriverstrust.org/volunteer; https://www.cranevalley.org.uk/.

Ensuring credible professional and CS survey and assessment results

The technical ground for observing rivers and collecting meaningful, high-quality data has been set over recent years but little attention has been paid to defining ‘rules’ or structuring collaborations. Staff in Rivers Trusts have received Defra-sponsored training in fluvial geomorphology but Trusts usually employ professional consultants for detailed project assessments and designs, especially in high-risk situations. Development of the CS-centric Modular River Survey ‘MoRPh’ and cRHS field survey methods (England et al., 2017; Gurnell et al., 2020; https://www.therrc.co.uk/crhs) offer the potential to resurrect process-related river form assessment such as GeoRHS, abandoned by statutory agencies (Branson et al., 2005; Walker et al., 2007). England and Gurnell (2016) highlight the impressive amounts of (web-based) publicly available ‘big data’ at a variety of geomorphological scales that can now form the essential backdrop context for CS survey work. Grabowski et al. (2014) hold the view that ‘restoration solutions can be developed that recognise the underlying drivers of geomorphic change and the constraints imposed on current fluvial processes’ (p. 483). MoRPh also has a very specific link to planning, development and land management under the UK policy of Biodiversity Net Gain (Gurnell et al., 2020).

Newson (2022: 411) stresses that, ‘realism concerning the consistency and legal standing of citizen science data is vital so as not to raise expectations’. The Catchment-based Approach, CaBA regularly stresses the governance and authenticity issues concerning CS (CaBA, 2015).

To ensure scientific credibility and a cost-effective deployment we suggest a formalised set of rules for physical habitat/hydromorphology. Table 2 shows seven tests for assessing the scientific credibility, compatibility and practical uptake of field survey methods, taking account of the eight generic principles for planning and deploying CS survey work set out by the EA (environmentagency-blog.gov.uk/2025/03/18/citizen-science-and-the-environment-agency). Full compliance represents the gold standard professional level, in this case represented by RHS. Table 3 illustrates the link between purpose and suitable field survey method, giving examples of proven methods and whether a CS approach could be suitable.

Table 2.

Seven generic tests of scientific credibility and practicality for professional-level physical habitat assessment work.

Test	Scientific/technical requirements	Practical considerations
Clarity of purpose	Project design suitable for specific output(s) and complementary to existing information and knowledge (see Table 3).	Proper project planning. End-user ownership. Participants’ skill sets. Partnership governance. Fully funded programmed timetable for survey work.
Valid methodology	Survey method, sampling strategy, sample unit, frequency and timing verified in relation to purpose and ‘proof of evidence’ level (#1).	Check sample sites for safety concerns. Implement safe working practice and secure landowner access permission where needed.
Confidence in quality assurance and control	Capabilities and limitations of field survey method (including adaptations) validated, benchmarked and calibrated.	Trained and accredited surveyors, supported by guidance manuals. Proven quality assurance/control protocols for accurate data collection. Data capture technology (forms, apps, photo/video images) tried and tested. Expert support available for surveyor queries.
Confidence in quality assurance and control	Supplementary data extraction from other databases (e.g. land use, geology, historical maps) for comprehensive contextual interpretation (#4).
Valid interpretation and outputs	Data analyses and diagnostics for indices and classifications validated, calibrated and derivations peer-reviewed and publicly available. Confidence levels defined for data and interpretation. Wherever possible, empirical evidence used to support expert opinion.	Availability of independent experts to verify interpretation. Multi-discipline project advisory group/network for peer review purposes.
Robust IT infrastructure and support	Logical checks and bug-fixing protocols to prevent erroneous outputs. Data collection technology tested for adverse conditions (bad weather, weak network signal); back-up available.	Data capture, database design, archive capacity and analytical tools compatible with end-user IT hardware and software. Project work included in end-user IT programme to ensure ongoing maintenance, fixes and upgrades.
Compatibility with existing databases	Interpretation and analytical capability (including AI performance) maximised by compatibility with existing databases and links to supplementary data (#3).	IT platform design capable of importing data from a variety of databases and exporting information to other end users.
Proven use of results	Results satisfy project objectives achieve favourable audit/peer review and improve knowledge.	Outputs used by practitioners for intended purpose and publicised, where relevant, for application elsewhere.

Table 3.

Seven generic categories of survey purpose and examples of field methods used.

Purpose	Scale, approach and data type	Examples of methods and their application	CS suitable?^a
Riverscape/meso-habitat scale state of environment reporting.	National/regional scale. Stratified random sampling for statistical validation. Quantitative.	RHS. Detecting impacts and trends in quality over time. Basis for context analysis supporting strategic EA and EIA.	No. Professional-level expertise required.
Characterisation and detecting change at reach/microhabitat scale	Reach/site scale.	MoRPh and cRHS. Catchment characterisation; MoRPh. Post-project appraisal (e.g. habitat restoration)	Yes. MoRPh, cRHS.
	Repeat ‘audit’ of river features to assess local change. Semi-quantitative.		Yes. MoRPh.
Fluvial morphology assessment	Catchment scale walkover to assess morphological processes and artificial impacts acting along the river network. Semi-quantitative.	Fluvial audit; GeoRHS.	No. Requires professional-level expertise for field survey.
		Establishes sediment transportation pathways.
		Essential background for flood management strategies and successful river restoration.
Research investigation	Postgraduate thesis work. Quantitative.	Specific experimental sampling to verify, corroborate and improve assumptions used in habitat quality and modification indices.	No, but metadata analysis could use CS derived data for testing assumptions and calibrating results.
Rapid surveillance	Gap-filling rapid walkover survey of unvisited headwaters. Qualitative.	Naturalness Assessment (priority habitats).	Yes. Naturalness Assessment. Professional follow-up required.
Rapid surveillance		Rapid assessment to locate sites of potential conservation interest, and habitat restoration.
Incident response	Rapid response initial site assessment of suspected illegal activity (e.g. unlicensed dredging). Qualitative.	Preliminary collection of photographic and other evidence prior to possible follow-up enforcement action.	Yes. Initial visit only. Professional follow-up visit required.
Education and public awareness	Simple, descriptive look-see site surveys suitable for schoolchildren and interested public. Qualitative.	Riverside Explorer surveys.	Yes. Several methods, including Riverside Explorer (Hawley et al., 2002).
Education and public awareness		Interactive teaching material demonstrates basic principles of river processes, river health and why rivers flood.

^aTo ensure scientific credibility, CS field methods require professional-level verification of results and interpretation.

The three CS-designed methods highlighted in Table 3 have recently been used (two in England, cRHS in Wales) but they are still under development. Although training has been developed, there is no coordinated deployment plan and no formal protocols for independent peer review, data-sharing, harmonising IT platforms and ways of demonstrating environmental benefits resulting from the work. All three would probably fail at least one of the EA’s guiding principles for CS partnership working. Above all, there is uncertainty about funding the survey work, and the associated costs of professional input needed for training, surveyor support, quality assurance and control and interpretation, IT development and dissemination pathways.

The crux of the matter is trust – and therefore use – of CS data by professional river scientists. To that end, we recommend that a special workshop/forum is convened, involving experts from different scientific disciplines, end-users, statutory and NGO professionals, environmental consultancies and CS surveyors, with the specific aims of considering how to harmonise deployment of CS for physical habitat assessment. This would build on the substantial background work generated by the CaSTCO project and European (CEN) guidance standards, plus early experience of CS surveys. It would make recommendations covering topics such as follows:

- independent peer review of data collection and interpretation;

- common standards on nomenclature and technical definitions;

- national and catchment sampling strategies for maximising use of existing data for harmonising planned and ad hoc surveys;

- technical specifications for different kinds of purpose-led surveys;

- independent provision of training and accreditation;

- compatibility of IT platforms for data transfer, interpretation and dissemination;

- securing critical mass and career development for professional scientists;

- long-term monitoring needs and associated deployment plan;

- best practice examples of uptake and use;

- a promotion plan to raise awareness of multiple stressor impacts and remedies;

- funding streams to deliver the above.

The outputs from these topics could be published as a series of papers in a special issue of a relevant journal, in the same fashion as those that provided the audit trail for method development and deployment of RHS and associated methods (Aquatic Conservation: special issue volumes 8(4),1998: 383-644; 12(4),2002: 327-483 and 20(Suppl. 1),2010: S1-S130).

Organisations such as CIWEM and CIEEM, plus RRC have an important role to play in developing a coherent, coordinated and credible CS contribution to monitoring the physical aspects of river health. Collective understanding and transparent standards of practice would provide reassurance for those commissioning work and build trust between professional scientists and CS volunteers. And, ultimately, improve the chances of environmental improvement that is the common objective of all concerned.

Conclusions

If multiple stressors on river systems are to be monitored and tackled in a coherent and efficient manner there are policy and resource implications for water management. Hydromorphological disruption is an important stressor but its profile and associated assessment and monitoring effort are low compared to water pollution. To restore river health fully in the long-term, redressing the current imbalance caused by the domination of tackling water pollution is needed. CS can play a powerful advocacy and operational role in that rebalance.

Better understanding of morphological (and especially hydrological) processes and disruption at local and broader scales is needed, plus monitored examples that prove beyond doubt the multiple benefits of habitat recovery work. Well-directed and suitably competent CS ‘monitoring’ can contribute to better understanding but more testing, calibration and harmonisation of methods are required to achieve the necessary confidence for wide (but standardised) uptake.

Several scientific, technical, IT and practical challenges need to be resolved to ensure optimum sharing of knowledge and use of resources. Above all, CS cannot and must not replace professional river science. We have made recommendations covering these challenges that would help to provide reassurance to the professional community, scientific and legal credibility and a feasible long-term monitoring strategy.

Whilst nationally identified targets for habitat protection and restoration are readily adopted by local, place-based, projects, involving fit-for-purpose CS involvement, it is vital that for scientific credibility and knowledge transfer, data are compatible with established survey and monitoring programmes and associated IT platforms. The EA’s encouragement of CS comes with, albeit latent, protocols, presumably to avoid a complex and costly legal situation with undisciplined evidence, however useful it is in drawing attention to a problem.

Ultimately, successful harmonisation of professional and CS effort will be determined by those organisations who commission monitoring surveys and use the results to improve river condition. Funding that deployment, especially in times of financial constraint, remains a major concern but that should not prevent all interested parties taking the opportunity to make progress on collective action.

Footnotes

Acknowledgements

Many of the insights, evidence and opinions gained for this paper derive from our participation as advisors to the CaSTCo project. We also acknowledge the help of the many colleagues who have helped us develop and apply systems of hydromorphological survey and assessment over the last 40 years. Special thanks for help with this paper go to Chris Mainstone, John Lewin and Pete Scarlett. We also gratefully acknowledge the help provided by two anonymous reviewers.

ORCID iD

Malcolm Newson

Ethical considerations

Neither is relevant to the research methods used: essentially literature-based and collaborative.

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: We received funding from the CaSTCo project () for advisory work to review hydromorphological methods in relation to suitability for citizen science participation. Our views are entirely personal and do not represent an output from the CaSTCo project.

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Data Availability Statement

Not relevant to this paper. We use public sources with appropriate acknowledgement.*

References

Acreman

(2016) Environmental flows – basics for novices. WIREs Water 3: 622–628.

Allen

(1994) The Naturalist in Britain. A Social History. Princeton University Press.

Barrett

Fleming

Taylor

, et al. (2024) A short-term home with long-term potential: temporary aquatic habitat additions to support macroinvertebrate colonisation. New Zealand Journal of Zoology 52: 934–943.

Belletti

Rinaldi

Buijse

, et al. (2015) A review of assessment methods for river hydromorphology. Environmental Earth Sciences 73: 2079–2100.

Bishop

Head

Shephard

, et al. (2021) The Role of Citizen Science in UK Freshwater Monitoring. Technical Report. Earthwatch Europe.

Boon

Holmes

NTH

Raven

(2010) Developing standard approaches for recording and assessing hydromorphology: the role of the European Committee for Standardization (CEN). Aquatic Conservation: Marine and Freshwater Ecosystems 20: S55–S61.

Bowler

Bhandari

Repke

, et al. (2022) Decision-making of citizen scientists when recording species observations. Scientific Reports 12: 11069.

Branson

Hill

Hornby

, et al. (2005) A Refined Geomorphological and Floodplain Component River Habitat Survey (Georhs). R&D Technical Report SC020024/TR. Environment Agency.

British Standards Institution (2004) Water Quality – Guidance Standard for Assessing the Hydromorphological Features of Rivers. BSI.

10.

Brooks

Fitch

Davy-Bowker

, et al. (2019) Anglers’ riverfly Monitoring Initiative (ARMI): a UK-wide citizen science project for water quality assessment. Freshwater Science 38(2): 270–280.

11.

Browne

(2024) The Work of the Environment Agency. Wildlife and Countryside Link. https://www.wcl.org.uk/

12.

Buss

Cai

Cardenas

(2009) The Hyporheic Handbook. A Handbook on the groundwater-surface Water Interface and Hyporheic Zone for Environmental Managers. Science Report SC050070. Environment Agency.

13.

Buytaert

Zulkafli

Grainger

, et al. (2014) Citizen science in hydrology and water resources: opportunities for knowledge generation, ecosystem service management, and sustainable development. Frontiers in Earth Science 2: 26.

14.

Catchment Based Approach Data User Group (2015) CaBA Monitoring Framework. (report of December 2015 meeting to Environment Agency Strategic Monitoring Review). https://www.catchmentbasedapproach.org/

15.

CEN (European Committee for Standardization) (2020) Water Quality – Guidance for Assessing the Hydromorphological Features of Rivers.

16.

Chesapeake Monitoring Cooperative (2020) Water Quality Monitoring. Rubric for Tier Determination and Inclusion of Data in the CMC Database.

17.

Colbert

(2022) Environment Agency Prosecutions 6% of the Level They Were a Decade Ago. Byline Times. https://www.bylinetimes.com/

18.

Collins

France

Walker

, et al. (2023) The potential for freshwater citizen science to engage and empower: a case study of the Rivers trusts, United Kingdom. Frontiers in Environmental Science 11: 1218055.

19.

Cresswell

McKinstry

Wolters

, et al. (2018) Five key strategic priorities of integrating patient generated health data into United Kingdom electronics health records. Journal of Innovation in Health Informatics 25(4): 254–259.

20.

Dawson

Ashmore

(2025) Quantifying geomorphic form variation for assessing habitat complexity of river restoration designs. Ecological Engineering 210: 107437.

21.

Defra (2024) Government response to the office for environmental protection report on the implementation of the water framework directive regulations and river basin management planning in England. In: Presented to Parliament Pursuant to Section 29 of the Environment Act 2021. Defra.

22.

Dent

Chadwick

DDA

Eagle

LJB

, et al. (2023) Microplastic burden in invasive signal crayfish (Pacifastacus lenuisculus) increases along a stream urbanization gradient. Ecology and Evolution 13: e10041.

23.

Dicks

Walsh

Sutherland

(2014) Organising evidence for environmental management decisions: a ‘4S’ hierarchy. Trends in Ecology & Evolution 29(1): 607–613.

24.

England

Gurnell

(2016) Incorporating catchment to reach scale processes into hydromorphological assessment in the UK. Water and Environment Journal 30: 22–30.

25.

Environment Agency (2010) The State of River Habitats in England, Wales and the Isle of Man.

26.

Environment Agency (2023) Science for the Environment: Excellent, Trusted, Applied.

27.

European Commission (2000) Directive 2000/60/EC of the European parliament and of the council of 23rd October 2000: establishing a framework for community action in the field of water policy. Official Journal of the European Communities L327: 1–72.

28.

European Environment Agency (2017) Surface Water Quality Monitoring Summary: The UK and International Monitoring Programmes. https://www.eea.europa.eu/publications

29.

European Environment Agency (2024) Europe’s State of Water 2024. the Need for Improved Water Resilience. EEA Report 07. https://www.eea.europa.eu/publications

30.

Everard

(2012) What have rivers ever done for us? ecosystem services and river ecosystems. In: Boon

Raven

(eds) River Conservation and Management. Wiley: pp. 313–324.

31.

Fox

PJA

Naura

Scarlett

(1998) An account of the derivation and testing of a standard field method: river habitat survey. Aquatic Conservation: Marine and Freshwater Ecosystems 8: 455–475.

32.

Fraisl

Hager

Bedessem

(2022) Citizen science in environmental and ecological sciences. Nature Reviews Methods Primers 2: 64.

33.

Freeman

Noble

Newson

, et al. (2007) Modelling population changes using data from different surveys: the common birds census and the breeding bird survey. Bird Study 54: 61–72.

34.

Gostner

Alp

Schleiss

, et al. (2012) The hydro-morphological index of diversity: a tool for describing habitat heterogeneity in river engineering projects. Hydrobiologia 712: 43–60.

35.

Gough

(2007) Weight of evidence: a framework for the appraisal of the quality and relevance of evidence. Research Papers in Education 22(2): 213–228.

36.

Gov.UK (2025) Environment Agency Chief Regulators Report, 2023–2024. https://www.gov.uk/government/publications/environment-agency-chief-regulators-report-2023-24/environment-agency-chief-regulators-report-2023-2024/

37.

Grabowski

Surian

Gurnell

(2014) Characterising geomorphological change to support sustainable river restoration and management. WIREs Water 1: 483–512.

38.

Gumiero

Veronesi

Gaetano Cirrone

, et al. (2025) The role of citizen science within WFD and SDGs, and how to incentivize the collaboration with environmental regulators. Open Research Europe 5: 45.

39.

Gurnell

Rinaldi

Belletti

, et al. (2016) A multi-scale hierarchical framework for developing understanding of river behaviour to support river management. Aquatic Sciences 78: 1–16.

40.

Gurnell

Scott

England

, et al. (2020) Assessing river condition: a multiscale approach designed for operational application in the context of biodiversity net gain. River Research and Applications 36: 1559–1578.

41.

Guston

(2023) Governing science, technology and innovation in hotter times. In: Orr

(ed) Democracy in a Hotter Time. Climate Change and Democratic Transition. MIT Press.

42.

Hawley

Raven

Anstey

, et al. (2002) Riverside explorer: an educational application of river habitat survey information. Aquatic Conservation: Marine and Freshwater Ecosystems 12: 457–469.

43.

HM Government (2018) A Green Future: Our 25 Year Plan to Improve the Environment. https://www.gov.uk/government/publications/independent-water-commission-review-of-the-water-sector

44.

HM Government (2023) Environmental Improvement Plan. First Revision of the 25 Year Environment Plans. Defra. https://www.gov.uk/government/publications/environment-improvement-plan

45.

HM Government (2025) Environment Agency Chief Regulator’s Report 2023-24. https://www.gov.uk/government/publications/environment-agency-chief-regulators-report-2023-24/2e06554f-6fca-4e39-85cf-561a7b143a4a

46.

House of Commons Environmental Audit Select Committee (2022) Water Quality in Rivers. Fourth Report of Session 2021-22. Report HC74. https://www.parliament.uk/eacom

47.

Jeffers

JNR

(1998) The statistical basis of sampling strategies for rivers: an example using river habitat survey. Aquatic Conservation: Marine and Freshwater Ecosystems 8: 447–454.

48.

Johns

Lindegarth

Carstensen

(2013) Establishing reference conditions and setting class boundaries. In: Deliverable 2.1-2, WATERS Report No. 2013:2. Havsmiljoinstitutet.

49.

Johnson

(2001) Defining reference conditions and setting class boundaries in ecological monitoring and assessment. REFCOND project Background Document: p. 13. https://www.oieau.fr/files/documents/195479_notice

50.

Johnson

Thorne

Castro

, et al. (2020) Biomic river restoration: a new focus for river management. River Research and Applications 36: 3–12.

51.

Jones

Murphy

Collins

, et al. (2012) The impact of fine sediment on macro-invertebrates. River Research and Applications 28: 1055–1071.

52.

Jones

Lloyd

CEM

Murphy

, et al. (2023) What do invertebrate indices measure? stressor-specific macroinvertebrate indices can be confounded by other stressors. Freshwater Biology 68: 1330–1345.

53.

Kucharski

(2025) Proof. the Uncertain Science of Certainty. Profile Books.

54.

Langford

Worthington

Shaw

, et al. (2012) The unnatural history of the river Trent: 50 years of ecological recovery. In: Boon

Raven

(eds) River Conservation and Management. Wiley: pp. 261–272.

55.

Lapointe

Rochman

Tufenkji

(2022) Sustainable strategies to treat urban runoff needed. Nature Sustainability 5: 366–369.

56.

Lave

(2012a) Fields and Streams: Stream Restoration, Neoliberalism, and the Future of Environmental Science. The University of Georgia Press.

57.

Lave

(2012b) Neoliberalism and the production of environmental knowledge. Environment and Society 3: 19–38.

58.

Lewis

Williams

(1984) Rivers and Wildlife Handbook. Sandy Beds: Royal Society for the Protection of Birds.

59.

Maddock

Harby

Kemp

, et al. (2013) Ecohydralics. An Integrated Approach. Wiley.

60.

Mainstone

(2016) Developing a coherent narrative for conserving freshwater and wetland habitats: experiences in the UK. WIREs Water 4: e1189.

61.

McCabe

Matthaei

Tonkin

(2025) The ecological benefits of more room for rivers. Nature Water 3: 260–270.

62.

Moss

(2015) Mammals, freshwater reference states, and the mitigation of climate change. Freshwater Biology 60(9): 1964–1976.

63.

Mosselman

Rinaldi

Garcia de Jalon

(2024) The European REFORM project for hydromorphological quality in river basin management. In: Rashed

(ed) Inland Waters – Ecology, Limnology and Environmental Protection. IntechOpen.

64.

Mulgan

(2020) When Science Meets Power. Polity.

65.

Nardi

Cudennec

Abrate

, et al. (2022) Citizens AND Hydrology (CANDHY): conceptualizing a transdisciplinary framework for citizen science addressing hydrological challenges. Hydrological Sciences Journal 67(16): 2534–2551.

66.

National Rivers Authority (1992) River corridor surveys. In: Conservation Technical Handbook 1. National Rivers Authority.

67.

Natural England (2015) River Restoration Theme Plan: A Strategic Approach to Restoring the Physical Habitat of Rivers in England’s Natura 2000 Sites. https://www.gov.uk/natural-england

68.

Newson

(2002) Geomorphological concepts and tools for sustainable river ecosystem management. Aquatic Conservation: Marine and Freshwater Ecosystems 12: 365–379.

69.

Newson

(2011) Rivers in trust: stakeholders and delivery of the EU water framework directive. Proceedings of the Institution of Civil Engineers - Water Management 164: 433–440.

70.

Newson

(2022) Fluvial geomorphology and environmental design’: restitution for damage, rehabilitation, restoration or rewilding? Earth Surface Processes and Landforms 47: 409–421.

71.

Newson

Large

ARG

(2006) ‘Natural’ rivers, ‘hydromorphological quality’ and river restoration: a challenging new agenda for applied fluvial geomorphology. Earth Surface Processes and Landforms 31: 1606–1624.

72.

Newson

Lewin

(2024) The developing flood rich period: science evidence and policy evolution for England. Is it time for place-based socio-ecological solutions? River Research and Applications 41: 1–21.

73.

Newson

(2000) Geomorphology, ecology and river channel habitat: mesoscale approaches to basin-scale challenges. Progress in Physical Geography 24(2): 195–217.

74.

Newson

Lewin

Raven

(2023) River science: an educational resource for understanding and learning to survive flooding and environmental change. Journal of Geography in Higher Education 48: 325–344.

75.

Office for Environmental Protection (2023) Progress in Improving the Natural Environment in England 2021/2022. https://www.gov.uk/official-documents

76.

Office for Environmental Protection (2024a) Progress in Improving the Natural Environment in England 2022/2023. https://www.gov.uk/official-documents

77.

Office for Environmental Protection (2024b) A Review of Implementation of the Water Framework Directive Regulations and River Basin Management Planning in England. https://www.gov.uk/official-documents

78.

O’Brien

(2024) Dirty Waters: How the Environment Agency Lost its Way. The Guardian. https://www.theguardian.com/environment/article/2024/jun/13/dirty-waters-how-the-environment-agency-lost-its-way?utm_term=676d4563c6100

79.

Palmer

Ambrose

Poff

(1997) Ecological theory and community restoration ecology. Restoration Ecology 5(4): 291–300.

80.

Palmer

Menninger

Bernhardt

(2010) River restoration, habitat heterogeneity and biodiversity: a failure of theory or practice? Freshwater Biology 55(Suppl. 1): 205–222.

81.

Papangelakis

Hassan

Luzi

, et al. (2023a) Measuring geomorphology in river assessment procedures 1: a global review of current practices. Journal of the American Water Resources Association 59: 1342–1359.

82.

Papangelakis

Hassan

Luzi

, et al. (2023b) Measuring geomorphology in river assessment procedures 2: recommendations for supporting river management goals. JAWRA Journal of the American Water Resources Association 59: 1–23.

83.

Petts

(1988) Regulated rivers in the United Kingdom. Regulated Rivers: Research & Management 2(3): 201–220.

84.

Pocock

MJO

Chapman

Sheppard

, et al. (2014) A Strategic Framework to Support the Implementation of Citizen Science for Environmental Monitoring. Final Report to SEPA. CEH Wallingford/Penicuik.

85.

Pocock

MJO

Hamlin

Christelow

, et al. (2023) The benefits of citizen science and nature-noticing activities for well-being, nature connectedness and pro-nature conservation behaviours. People and Nature 5: 591–606.

86.

Pursglove

(1988) Taming the Flood. 2nd edition 2017. Harper Collins, Oxford University Press.

87.

Keller

Bachiller-Jareno

, et al. (2023) Significant improvement in freshwater biodiversity in all types of English rivers over the past 30 years. Science of the Total Environment 905: 1–13.

88.

Hutchins

Fitch

, et al. (2025) River invertebrate biodiversity benefits from upstream urban woodland. Landscape and Urban Planning 254: 1–12.

89.

Raven

George

(1988) Recovery by riffle macroinvertebrates in a river after a major accidental spillage of chloropyrifos. Environmental Pollution 59: 55–70.

90.

Raven

Holmes

NTH

Dawson

, et al. (1998a) River Habitat Quality. the Physical Character of Rivers and Streams in the UK and Isle of Man. Environment Agency.

91.

Raven

Holmes

NTH

Dawson

, et al. (1998b) Quality assessment using river habitat survey data. Aquatic Conservation: Marine and Freshwater Ecosystems 8: 477–499.

92.

Rimmert

Baudoin

Cotta

, et al. (2020) Participation in river basin planning under the water framework directive – has it benefitted good water status? Water Alternatives 13(3): 484–512.

93.

Rinaldi

Surian

Comiti

, et al. (2013) A method for the assessment and analysis of the hydromorphological condition of Italian streams: the morphological Quality Index (MQI). Geomorphology 180-181: 96–108.

94.

Robins

Naura

Austin

, et al. (2025) A new framework for river restoration planning at catchment scale in the UK. River Research and Applications 41: 82–107.

95.

Robinson

Cawthray

West

Bonn

Ansine

(2018) Ten principles of citizen science. In: Hecker

(ed) Innovation in Open Science, Society and Policy. University College Press: pp. 27–40.

96.

Roger

Anstee

Ogashawara

, et al. (2024) Editorial: environmental citizen studies in freshwater science. Frontiers in Environmental Science 12: 1450224.

97.

Seager

Baker

Parsons

, et al. (2012) The rivers and streams of England and Wales: an overview of their physical character in 2007-2008 and changes since 1995-1996. In: Boon

Raven

(eds) River Conservation and Management. Wiley, 29–44.

98.

Sear

(2023) We Have Forgotten what a ‘Natural’ River Even Looks like. The Conversation. https://theconversation.com/we-have-forgotten-what-a-natural-river-even-looks-like/

99.

Sear

Thorne

Newson

(2010) Guidebook in Applied Fluvial Geomorphology. Thomas Telford.

100.

Sedell

Reeves

Hauer FH Stanford

, et al. (1990) Role of refugia in recovery from disturbances: modern fragmented and disconnected river systems. Environmental Management 14(5): 711–724.

101.

Shao

Bishop

(2025) Citizen science in river monitoring: a systematic literature review of the whys and hows. Frontiers in Environmental Science 13: 1609084.

102.

Shuker

Gurnell

Wharton

, et al. (2017) MoRPh: a citizen science tool for monitoring and appraising physical habitat changes in rivers. Water and Environment Journal 31: 418–424.

103.

Shuker

Gurnell

Hull

(2024) Biogeomorphological response to river restoration of a suburban river with large wood: creating a restoration vision and cost-effectively monitoring the response trajectory using the citizen science MoRPh survey. River Research and Applications 40(6): 1106–1124.

104.

SNIFFER (2006) Development of environmental standards (water resources). In: Stage 3: Environmental Standards. SNIFFER.

105.

SNIFFER (2012) Ecological Indicators of the Effects of Abstraction and Flow Regulation; and Optimisation of Flow Releases from Water Storage Reservoirs. SNIFFER.

106.

SSWAN (2025) Sustainable Solutions for Water and Nature. Discussion Paper. Green Alliance.

107.

Sutherland

(ed) (2022) Transforming Conservation. A Practical Guide to Evidence and Decision Making. Open Book Publishers.

108.

Szalkiewicz

Sucholas

Grygoruk

(2020) Feeding the future with the past: incorporating local ecological knowledge in river restoration. Resources 9: 47.

109.

Theodoropolous

Stamou

Vardakas

, et al. (2020) River restoration is prone to failure unless pre-optimized within a mechanistic ecological framework. Insights from a model-based case study. Water Research 173: 115550.

110.

Thorp

Thoms

Delong

(2006) The river ecosystem synthesis: biocomplexity in river networks across space and time. River Research and Applications 22: 123–147.

111.

Tweddle

Robinson

Pocock

MJO

, et al. (2012) Guide to Citizen Science: Developing, Implementing and Evaluating Citizen Science to Study Biodiversity and the Environment in the UK. Natural History Museum and NERC Centre for Ecology & Hydrology for UK‐EOF.

112.

United States Environmental Protection Agency (1996) The Volunteer Monitor’s Guide to Quality Assurance Project Plans. EPA 841-B-96-003.

113.

University of Manchester (2022) The future of patient-generated data for UK health research. In: Report from a Roundtable Event. Centre for Epidemiology Versus Arthritis.

114.

Van der Heijden

ten Heuvelhof

(2012) The mechanics of virtue: lessons on public participation from implementing the water framework directive in the Netherlands. Environmental Policy and Governance 22: 177–188.

115.

Vaughan

Diamond

Gurnell

, et al. (2009) Integrating ecology with hydromorphology: a priority for river science and management. Aquatic Conservation: Marine and Freshwater Ecosystems 19: 113–125.

116.

Vermaat

Wagtendonk

Brouwer

, et al. (2016) Assessing the societal benefits of river restoration using the ecosystem services approach. Hydrobiologia 769: 121–135.

117.

Vezza

Goltara

Spairani

, et al. (2015) Habitat indices for rivers: quantifying the impact of hydro-morphological alterations on the fish community. In: Lollino

(eds) Engineering Geology for Society and Territory. Springer, Vol. 3: pp. 357–360.

118.

Vohland

Land-Zandstra

Ceccaroni

Lemmens

Perello

Ponti

Samson

Wagenknecht

(2021) Editorial: the science of citizen science. In: Vohland

(ed) The Science of Citizen Science. Springer.

119.

Walker

Diamond

Naura

(2002) The development of physical quality objectives for rivers in England and Wales. Aquatic Conservation: Marine and Freshwater Ecosystems 12: 381–390.

120.

Walker

Gibson

Brown

(2007) Selecting fluvial geomorphological methods for river management including catchment scale restoration within the environment agency of England and Wales. International Journal of River Basin Management 5(2): 131–141.

121.

Ward

Holmes

Jose

(1994) The New Rivers and Wildlife Handbook. Royal Society for the Protection of Birds. ISBN 10: 0903138700⁄ISBN 13: 9780903138703.

122.

West

Van Kleek

Giordano

, et al. (2017) Information quality challenges of patient-generated data in clinical practice. Frontiers in Public Health 5: 284.

123.

Whelan

Linstead

Worrall

, et al. (2022) Is water quality in British rivers ‘better than at any time since the end of the industrial revolution’? The Science of the Total Environment 843: 157014.

124.

White

Amano

Boersch-Supan

, et al. (2022) Gathering and assessing pieces of evidence. In Sutherland

(ed) Transforming Conservation. A Practical Guide to Evidence and Decision Making. Open Book Publishers.

125.

Wilkes

Mungee

Naura

, et al. (2024) Predicting nature recovery for river restoration planning and ecological assessment: a case study from England, 1991–2042. River Research and Applications 41: 68–81.

126.

Wilkinson

Boxall

ABA

Kolpin

, et al. (2022) Pharmaceutical pollution of the world’s rivers. Proceedings of the National Academy of Sciences of the United States of America 119: 8.

127.

Wohl

Lane

Wilcox

(2015) The science and practice of river restoration. Water Resources Research 51(8): 5974–5997.

128.

Woodward

Rothwell

, et al. (2021) Acute riverine microplastic contamination due to avoidable releases of untreated wastewater. Nature Sustainability 4: 793–802.

129.

Yeung

DY-L

Jiang

Warner

, et al. (2024) The effects of volunteering on loneliness among lonely older adults: the HEAL-HOA dual randomised control trial. The Lancet. Healthy Longevity 6: 100664.

Professional and citizen science to monitor and improve the physical habitat quality of rivers

Abstract

Keywords

Introduction

Context: Why does water quality dominate river health assessment?

Box 1. Impacts of funding cuts on EA activity

The lure of citizen science: A ‘cheap’ policy response to a crisis?

Semantic precautions in a diverse field of public environmental engagement

Principles for monitoring and assessment of physical habitat

‘Natural’ river form and process: A template for repairing physical damage?

Hydromorphological factors within the panoply of multiple stressors

Restoration and river system resilience: Longer-term opportunities for CS

Ensuring credible professional and CS survey and assessment results

Conclusions

Footnotes

Acknowledgements

ORCID iD

Ethical considerations

Funding

Declaration of conflicting interests

Data Availability Statement

References