The recovery of European freshwater biodiversity has come to a halt

Owing to a long history of anthropogenic pressures, freshwater ecosystems are among the most vulnerable to biodiversity loss(1). Mitigation measures, including wastewater treatment and hydromorphological restoration, have aimed to improve environmental quality and foster the recovery of freshwater biodiversity(2). Here, using 1,816 time series of freshwater invertebrate communities collected across 22 European countries between 1968 and 2020, we quantified temporal trends in taxonomic and functional diversity and their responses to environmental pressures and gradients. We observed overall increases in taxon richness (0.73% per year), functional richness (2.4% per year) and abundance (1.17% per year). However, these increases primarily occurred before the 2010s, and have since plateaued. Freshwater communities downstream of dams, urban areas and cropland were less likely to experience recovery. Communities at sites with faster rates of warming had fewer gains in taxon richness, functional richness and abundance. Although biodiversity gains in the 1990s and 2000s probably reflect the effectiveness of water-quality improvements and restoration projects, the decelerating trajectory in the 2010s suggests that the current measures offer diminishing returns. Given new and persistent pressures on freshwater ecosystems, including emerging pollutants, climate change and the spread of invasive species, we call for additional mitigation to revive the recovery of freshwater biodiversity.

Automated summary

Due to historical anthropogenic pressures, freshwater ecosystems are highly vulnerable to biodiversity loss. Mitigation efforts, such as wastewater treatment and hydromorphological restoration, aim to improve environmental quality and restore freshwater biodiversity. This study analyzed 1,816 time series of freshwater invertebrate communities across 22 European countries from 1968 to 2020. The findings reveal overall increases in taxonomic and functional diversity and abundance, but these increases have plateaued since the 2010s. Communities downstream of dams, urban areas, and croplands show lower chances of recovery. Faster rates of warming are associated with lesser gains in biodiversity. Additional mitigation measures are needed to revive the recovery of freshwater biodiversity in response to emerging pollutants, climate change, and invasive species.