Evidence charts the future of freshwater biodiversity conservation

Evidence is essential for promoting freshwater conservation and selecting appropriate conservation actions. This article examines the importance of evidence for freshwater conservation, available sources, how evidence is used, geographical coverage, and the challenges in obtaining evidence. Two databases containing published evidence, namely, Conservation Evidence (CE) and the Collaboration for Environmental Evidence (CEE), were systematically searched and evaluated. Evidence in CE is geographically skewed, with most studies coming from North America and Europe. The IUCN Red List requires evidence to assign species to threat categories, but is limited in its ability to track conservation success. IUCN Green Status can be used to assess the impact of conservation actions on species recovery, but suffers from some of the limitations of Red List assessments. Evidence is also required to select freshwater areas for protection, and for monitoring their condition over time, accompanied by an increasing recognition of the value of using evidence from Indigenous communities to support international agreements. Persistent barriers to the use of evidence for promoting freshwater conservation include weak baselines, short monitoring horizons, mismatched spatial scales, reliance on subjective opinion when analysing evidence, and under-reporting of failures. These and other barriers are addressed in several concluding recommendations.