Hot Weather Causes Massive Die-Off Of Smelt Thousands Of Tiny Fish Lost In Too-Warm Lake Washington

It hasn’t been hot enough in the Puget Sound area this summer to fry eggs on the sidewalk.

But summer heat has boosted the temperature in Lake Washington high enough to kill thousands of smelt.

“It’s like a bathtub out there, and the fish aren’t conditioned for that type of water,” said spokesman Larry Altose with the state Department of Ecology.

The dead fish - the adults are only about 4 inches long - are floating along the lake’s eastern shores, from Kirkland to the Interstate 90 East Channel Bridge, providing a feast for seagulls, crows and other scavengers.

Area temperatures, in the high 80s and low 90s since mid-July, have raised water temperatures in some parts of the lake to nearly 80 degrees. That causes oxygen levels near the shore to plummet - a tough situation for sensitive smelt.

“This happens from time to time in freshwater lakes,” Altose said. “When water conditions are right, fish can be deprived of oxygen and they die.”

“It’s not strictly the heat necessarily. There are numerous factors,” he said. But “so far as we can tell, pollution is not one of them. … It seems to be natural.”

Other species of fish are suffering as well. Biologists testing the waters off Enatai Beach in Bellevue on Thursday found a handful of dead perch and sticklebacks.

The Department of Ecology has received no reports of dead fish in other parts of the lake. Some biologists speculate that the problem is the larger amount of weeds on the east side of the lake. Some water plants suck in oxygen at night, they say.

Scientists with Ecology and King County will keep testing the lake. But solving the problem is likely just a matter of waiting for the weather to cool down, Altose said.

High lake temperatures in 1985 and 1977 also caused massive smelt kills, and Altose said some fish deaths were noted last year, as well.

But there are between 25 million and 30 million Lake Washington longfin smelt in the lake, so the deaths of several thousand will likely have little effect, said Tom Sibley, a University of Washington fisheries professor.

Bellevue parks officials decided Thursday the fish kill did not warrant closure of the city’s beaches.