The Pyrenean desman (Galemys pyrenaicus), a rare, semi-aquatic mammal found only in the Pyrenees and the northwest of the Iberian Peninsula, is being tracked using environmental DNA (eDNA) collected from water samples in the torrents of Vicdessos in Ariège, France. This technique has become increasingly important as direct sightings of the species have grown rarer. The desman, a member of the mole family, has seen its range shrink by more than half over the past 30 years, according to the French Office for Biodiversity. It is currently classified as vulnerable on the IUCN Red List of threatened species, which identifies species at risk of endangerment. The decline in the desman's habitat is linked to several human-driven factors, including the artificial modification of riverbanks, the construction of hydroelectric dams, and the spread of pollution. Traditional methods of detecting the species—such as using footprint rafts, dung tunnels, and radio-tracking—have been employed, but they are time-consuming and depend on the chance of encountering the animal. In contrast, eDNA analysis has proven to be a more efficient and less disruptive way to confirm the species' presence. The detection of eDNA in water samples provides evidence that the Pyrenean desman is present in a given area and can serve as an indicator of the ecological health of mountain torrents. The presence of the desman’s genetic material in the water suggests that the watercourse maintains a high enough ecological quality to support this sensitive species. On the other hand, the absence of genetic traces in areas that were once suitable for the desman signals the ongoing degradation of these high-altitude aquatic environments. The LIFE+ Desman program, funded with over 2.6 million euros, is part of a broader European effort to protect the species across eleven Natura 2000 sites in the Pyrenees. The initiative involves a network of partners, including the Conservatoire d'espaces naturels Midi-Pyrénées, the Parc naturel régional des Pyrénées Catalanes, the Association des naturalistes ariégeois, and the Parc national des Pyrénées. The program aims to improve the long-term survival of the Pyrenean desman and guide conservation efforts by identifying areas where interventions will have the most impact. Using eDNA analysis allows researchers to cover large sections of hydrographic basins without disturbing the animal or its habitat. These findings also highlight the fragility of mountain torrent ecosystems, emphasizing the importance of preserving these environments not only for the Pyrenean desman but also for many other species that depend on such habitats.