About 200 dead adult steelhead have been found just below the Dworshak Dam on the North Fork of the Clearwater River in Idaho during the past week, according to the Corps of Engineers.
The Clearwater River joins the Snake River near the Idaho and Washington state line.
U.S. Fish and Wildlife Service staff at the Dworshak Fish Hatchery determined the steelhead likely hit structures of a turbine unit at the dam, according to the Corps.
Their injuries coincide with an upgrade of a turbine at the dam. The Corps said it would continue to investigate the exact cause of the fish deaths.