Downstream Fish Passage at High Head Dams

Restoring anadromous fish populations above hydroelectric dams is challenging to fishery managers because dams present barriers for both upstream- and downstream-migrating fish in a river system. Generally, dams were constructed with fishways to provide routes for upstream-migrating fish to pass them and, in general, downstream-migrants must pass dams by way of turbines, spillways, sluiceways, or bypass systems.  High-head dams present additional challenges for downstream fish passage because of the height of the dams, changes in river flows, and fluctuating reservoir elevations (sometimes over 35 m or more).  Downstream migrants must pass these high-head dams volitionally by way of turbines and spillways, or by collection and bypass systems. Some high head dams implement surface collectors and transport as a means to pass downstream migrating fish while others implement collectors and bypass pipes.