Measures for improving water quality to bend the curve of global freshwater biodiversity loss

The degradation of water quality is among the most pervasive, complex and challenging problems that impact the world's freshwater ecosystems and their biodiversity. Contamination pathways vary globally and involve a diverse array of pollutants that include simple (e.g. road salt) to more complex (e.g. pharmaceuticals) chemicals, as well as non-natural sources of heat, light, noise, silt, plastics and also pathogens from wastewater or livestock. These pollutants can cause significant harm on their own, in mixtures or in combination with other stressors. Over geographically extensive areas affecting most river systems and many standing waters, pollutants have been released either legally, illegally or incidentally over inter-decadal to centennial timescales. Some pollutants and pathogens also affect people through morbidity, mortality and economic loss, so that there is synergy in protecting freshwater biodiversity against pollution while delivering human well-being through the global Sustainable Development, ecosystem services and climate change agenda. Existing approaches aimed at reducing water pollution are insufficient and require a previously unmatched step-change in approach to address the major impacts from both conventional and emerging pollutants, such as pharmaceuticals, pesticides and microplastics. Success stories on measures that address freshwater pollution are relatively limited such that available examples are often "works in progress" or represent partial success. Here, we review both challenges and potential solutions to freshwater pollution, focusing on case studies that range across i) informing action through monitoring and understanding pollutant trends and ecosystem impacts; ii) regulation and enforcement nationally and internationally to reduce pollutant loads, substitute harmful substances and ensure that polluters pay; iii) improving the management and remediation of pollutants at source, in situ and across catchments, including scaleable, nature-based solutions and iv) addressing the systemic drivers of pollution through education, incentives and market mechanisms. Significant challenges remain, but water quality restoration in freshwater ecosystems will bring manifold benefits for freshwater biodiversity and human well-being at all scales from local to global.