King County health officials have closed eight beaches to swimmers after water samples revealed dangerous bacteria levels and toxic algae contamination, limiting recreational options as late summer temperatures reach the high 80s.
The affected locations include Madison Park Beach, Houghton Beach, Gene Coulon Beach, Newcastle Beach, Echo Lake Beach, Cottage Lake, Green Lake East, and Green Lake West beaches. King County Public Health collected water samples on September 9, 15, and 16 that exceeded safety thresholds.
“We test the water for bacteria, which tells us whether there is poop in the water from people, pets, or wildlife. Poop can carry germs that can make people sick from swimming or playing in the water,” the agency stated in a news release.
Health officials use Colony Forming Units (CFU) to measure bacterial contamination, counting bacteria per 100 milliliters of water. A beach is deemed contaminated when two or three samples exceed 320 CFUs on the same day.
Several beaches recorded dramatically elevated levels. Newcastle Beach initially showed the most severe contamination, with Sample A reaching 2,500 CFUs, eight times the safety threshold, and Sample B hitting 4,100 CFUs, nearly 13 times higher than acceptable levels.
Other concerning readings include Madison Park Beach at 760 CFUs and Houghton Beach samples ranging from 500 to 720 CFUs. Gene Coulon Beach recorded levels between 340-390 CFUs, while Newcastle Beach’s latest sample showed 330 CFUs.
Four locations, Echo Lake Beach, Cottage Lake, Green Lake East, and Green Lake West, were closed due to toxic algae rather than bacterial contamination.
“We use the bacteria test results to predict the chance that people will get sick from germs that might be in the water,” King County Public Health explained. “Instead of testing for each type of germ, we test for one type of bacteria that is easy to measure and commonly used to predict swimming-related illness risk.”
Despite the closures, several beaches remain open for public use, including Madrona Beach, Seward Park, Magnuson Beach, Meydenbaur Beach, and Enatai Beach.
The timing coincides with renewed summer heat, creating demand for water recreation just as safety concerns limit options. Health officials have not specified how long the closures will remain in effect.
The widespread contamination reflects ongoing challenges with water quality in King County’s recreational areas, where runoff from urban development, pet waste, and wildlife can contribute to bacterial contamination that poses health risks to swimmers.
