How big can a fish be and still pass through the Restoration Hydro Turbine (RHT) safely? Pretty big!
This article in French explains how Natel's FishSafe™ Restoration Hydro Turbine provides a solution for hydropower plants to coexist with migrating fish.
Abe Schneider and Sterling Watson lay out the argument for FishSafe™ turbines in this paper published in The International Journal of Hydropower & Dams, Issue 5.