This paper explores how traditional environmental concepts operate as a form of truth environmentality in conservation governance. Drawing on ethnographic research on tidal flat tourism in Jeungdo, South Korea, it focuses on the traditional concept of saengmyung (life) as a truth claim that shapes tidal flat conservation by rendering particular human-tidal flat relations morally intelligible and difficult to contest. This paper makes two main arguments. First, it demonstrates that saengmyung functions as a form of truth environmentality by framing tidal flats as habitats of life deserving respect, thereby legitimising conservation-oriented conduct. Second, it shows that saengmyung-based truth environmentality simultaneously stabilises and destabilises conservation governance: while it supports biodiversity conservation and recognition of local fishing practices, it also legitimises tourists’ leisure-catching activities, generating tensions within conservation regimes. This paper relates these ambivalent effects to the operation of truth environmentality within specific institutional settings, and to its mechanism that organises fields of judgement, rather than directly prescribing behaviours. By foregrounding both the governing potential and vulnerability of culturally grounded environmental truths, this paper contributes to recent work on truth and multiple environmentalities.