Humans have coexisted with animal species throughout history. Local Ecological Knowledge (LEK) refers to the body of knowledge, practices, and perceptions that people hold regarding the wild animals with which they share their environment. The huillín (Lontra provocax) is an endangered otter species. This study explores the LEK held by residents of Nahuel Huapi National Park and its surroundings concerning the natural history of the huillín, and analyzes how such knowledge varies according to sociocultural characteristics. Using a snowball sampling approach, we conducted semi-structured and open-ended interviews to gather LEK about the huillín. Based on variables identified in previous studies, we formulated hypotheses and developed five Generalized Linear Models to evaluate the relationship between LEK and the sociocultural characteristics of the interviewees. The results reveal nine local names for the huillín. The most extensive and detailed LEK comes from rural inhabitants. Forty percent of participants perceived a decline in the species’ abundance—citing threats from tourism to climate change—while none reported an increase. Personal testimonies of encounters with the species often supported these observations. The LEK held by those who coexist with the huillín provides original insights that can complement scientific knowledge. This approach fosters collective care networks that substantially reinforce the biocultural conservation of the huillín.