Lake Washington Fish Die-off May be a Natural Occurence, Say Officials

Elements of this story were originally reported by Jeanne Gustafson

Dozens of dead fish have been washing up on Mercer Island beaches in the past two weeks, but state and local officials say it's probably due to a natural migratory cycle — and not the result of pollution.

The tiny fish — no bigger than fingerlings at 2-4 inches long — are likely adult three-spine sticklebacks who have completed their spawning in Lake Washington, Mercer Island Parks Director Bruce Fletcher said.

"I am not an expert on stickleback die offs, but it appears to be nature taking its course," said Fletcher. Lifeguards are pulling little Sticklebacks from the beaches at both Groveland and Luther Burbank Park's beaches.

Officials from the State Department of Ecology and the Department of Fish & Wildlife (DFW) said that sticklebacks are a predominant species in Lake Washington and — similar to salmon — spawn annually, followed by a natural die-off that leaves a mass of dead fish in the lake, usually between about mid-June and early July. The phenomenon is natural and not indicative of a problem in the lake, said Ecology spokesperson Larry Altose.

"They are frequently found in conditions that we're having now," he said. "Those are males that have spawned and are typically seen at this time of year."