County scientists believe a toxic algae bloom is to blame for a large fish kill in Quartermaster Harbor last week.

The algae bloom is not harmful to humans and is not a result of pollution or high nitrogen levels in the harbor, said Doug Williams, a spokesman for the King County Department of Natural Resources.

“It just happens,” he said. “It’s a naturally occurring algae bloom.”

Williams said the bloom was a result of the recent warm weather and would die down as the weather changed.

“There’s nothing to do about it other than just wait,” he said.

Hundreds of small, dead shiner surfperch were discovered in Quartermaster Harbor late last week. Following up on a tip from a Vashon resident, scientists with the county’s Environmental Laboratory visited the harbor and collected water samples, which revealed dense concentrations of a phytoplankton that has been linked to fish kills.

County officials say that while the algae often blooms in Puget Sound during the warm summer months, sometimes causing colored water, most blooms are not concentrated enough to kill fish. However, there have been several large blooms in recent years that did result in fish kills.

People who observe colored water near dead fish are asked to contact SoundToxins at soundtox@uw.edu.