Toxic algae bloom prompts ‘stay out of the water’ warning at Green Lake

A “stay out of the water” advisory was issued for Green Lake after recent testing revealed toxic algae concentrations above state guidelines.

Public Health — Seattle and King County (KCPH) officials have recommended that people and pets not swim or drink from the lake, and avoid any other activities that involve making contact with the water, KCPH announced.

Toxic algae bloom located in Seattle’s Green Lake

The testing was conducted on May 11, and collected samples that relate to cyanobacteria blooms, which can produce toxins at levels that are harmful to humans, pets, domestic animals, and wildlife.

The department noted that cyanobacteria species can regulate their buoyancy and often rise to the water’s surface, forming a “surface scum.”

“A scum is a thin, oily-looking film that can become several inches thick (and can sometimes look like spilled paint),” KCPH stated.

When cyanobacteria bloom conditions are good, a lake or pond can change from clear to cloudy and murky within a matter of days.

Most cyanobacterial blooms tend to occur during warm summer months and early fall, though in Washington, toxic blooms can occur during the colder winter months.

The department noted a specific example in Pierce County’s American Lake, which has a history of toxic episodes during the winter at water temperatures as low as 44 degrees.

High bacteria samples shut down 3 King County beaches

Last week, high bacteria detections were found at three King County beaches, including Madison Park Beach, Gene Coulon Beach, and Seward Park/Andrews Bay Beach. Since then, all three beaches have returned to normal bacteria levels, and the “stay out of the water” advisories were lifted.

Gene Coulon Beach recorded two bacteria samples noticeably higher than the normal threshold. One sample revealed 14,000 Colony Forming Units (CFU), which is a count of the number of bacteria per 100 mL of water (about a half-cup of water).

A beach is deemed contaminated with bacteria if two or three samples return a result of more than 320 CFUs on the same day. Gene Coulon Beach was nearly 44 times higher than King County’s baseline for a contaminated beach.

“We use the bacteria test results to predict the chance that people will get sick from germs that might be in the water. There are many different types of germs that can come from poop (bacteria, viruses, parasites, etc.), and it is not possible to test for each one,” Public Health wrote. “Instead, we test for one type of bacteria that is easy to measure and is commonly used to predict the risk of getting sick from swimming.”

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