Experimental comparison of fish mortality and injuries at innovative and conventional small hydropower plants.
Resolving the controversy about hydropower is only possible based on reliable data on its ecological effects, particularly fish welfare. Herein, we propose a comprehensive assessment of conventional and innovative hydropower using a dataset of 52,250 fish. The effects of hydropower on fish were most harmful at sites with Kaplan turbines, showing ≤ 83% mortality. Innovative hydropower, often termed 'fish-friendly', caused ≤ 64% mortality. Our findings suggested that the runner peripheral speed, number of turbine blades and turbulence at turbine outlets were the most important factors. Synthesis and applications. To reduce the impact of hydropower on fish, site-specific characteristics such as head drop, bypass options and river-specific species composition need to be more intensively considered in optimal turbine technologies and operation modes.