Thousands of fish found dead in Spokane River. No one knows why

Wildlife officials are investigating the mysterious deaths of thousands of fish that were found floating in the Spokane River earlier this month.

"We have no idea why this happened," Jule Schultz, the waterkeeper for the Spokane Riverkeeper told the Spokesman-Review. "What we do know is this appeared to be a very large event."

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The fish were discovered at Long Lake Dam in Spokane, Washington, on Feb. 7. A former Long Lake Dam employee, Tom McClellan, came upon the scene while walking with his dog and reported it to the Spokane Tribe Fisheries and Water Resource Division.

"[I] looked down the hill, and there were literally thousands of fish right along the shore there," McClellan told KXYL News.

Most of the fish affected were walleye and perch as well as some salmonid species such as whitefish and trout. Local wildlife agencies didn't have an immediate explanation for the mysterious mass death.

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"[It] certainly has never happened in the 10 years that I've been working for the Spokane Riverkeeper," Schultz told KXYL News.

Chris Donley, Department of Fish and Wildlife’s Eastern region fish program manager, told the Spokesman-Review that officials have ruled out low levels of dissolved oxygen, a common factor in fish kills, and are waiting on test results to see if disease or some sort of contaminant is behind the deaths.

Biologists with the Spokane Tribe’s fisheries department sent samples to the Washington Animal Disease Diagnostic Laboratory for testing.

The region's ongoing effort to reintroduce salmon into the Spokane River makes the high death count even more concerning, Schultz said. 

"It’s a lot of fish and this is rare," he told KXLY News. "If it does indicate a problem with our river, we need to track that down and figure it out."