Evident but context-dependent mortality of fish passing hydroelectric turbines.

Globally, policies aiming for conservation of species and free flowing rivers and for promoting hydroelectricity as renewable energy and means to decarbonize energy systems generate trade-offs between protecting freshwater fauna and continuing development of hydropower. Hydroelectric turbines put fish at risk of severe injury during passage. Therefore, comprehensive, reliable analyses of turbine-induced fish mortality are pivotal to support an informed debate on the sustainability of hydropower, i.e., how much a society is willing to pay in terms of costs incurred on rivers. Our work examines the so far most comprehensive, global dataset of empirical turbine mortality assessments comprising >275,000 individual fish of 75 species. We show that hydroelectricity generation causes an overall average fish mortality of 22.3%, with a 95% confidence interval between 17.5 and 26.7%, while accounting for common variation and uncertainties related to empirical estimates. Mortality estimates were highly variable among and within different turbine types, study methods, and taxa. Our findings also identify technical configurations of hydroelectric turbines that successfully reduce fish mortality. We emphasize that fish-protective hydropower operation as a global standard could balance the needs for renewable energy with those of fish biodiversity protection. This article is protected by copyright. All rights reserved.