Various steps were taken in France during the Nineties to minimize the impact of hydroelectric power installations on fish migration downstream, focusing first on Atlantic salmon and later on the European eel. Following studies aimed at quantifying mortality among juvenile salmonids due to turbines, experiments were undertaken to fine-tune downstream bypasses to prevent passage of fish through the turbines. This led to the design of surface bypasses used conjunction with the existing trashracks at plant intakes, for which the design criteria and limitations are presented here.