CLEARWATER COUNTY, Idaho --- The U.S. Army Corps of Engineers is investigating after around 200 dead fish were discovered near one of the organization’s dams on the Clearwater River.

In a release, the U.S. Army Corps of Engineers confirms about 200 dead adult steelhead were discovered in a tailrace just below the Dworshak Dam on the North Fork of the Clearwater River.

Officials said the cause of the fish casualties is still under investigation, though they believe it has something to do with “non-routine upgrades of the dam’s turbine unit.”

The U.S. Army Corps of Engineers officials said they requested an assessment from the U.S. Fish and Wildlife Service Staff at the Dworshak Fish Hatchery, which found the steelhead mortalities were “likely caused by contact with structural features of the turbine unit.”

Officials said they will work with federal and state agencies, as well as other regional fish managers to further investigate the fish kill.