High bacteria levels prompt closures at 2 King County beaches
Jun 10, 2026, 2:30 PM | Updated: 2:34 pm
A sign warns people to stay out of the water. (Photo: Joe Raedle, Getty Images)
(Photo: Joe Raedle, Getty Images)
As the summer heat ramps up in the region, health officials warned that two King County beaches have returned high bacteria samples, urging beachgoers to stay out of the water.
High bacteria detections were found at Mount Baker Beach and Matthews Beach, Public Health — Seattle and King County announced.
High bacteria levels at 2 King County beaches
Public Health collected three water samples from separate parts of each beach on June 1 and 8, and the samples recorded high bacterial levels at each beach.
“We test the water for bacteria, which tells us whether there is poop in the water from people, pets, or wildlife,” the department stated. “Poop can carry germs that can make people sick from swimming or playing in the water.”
Public Health based its decision on the number of colony-forming units (CFU) found, which is a count of bacteria per 100 mL of water (about half a cup), according to King County.
A beach is deemed contaminated with bacteria if two or three samples return a result of more than 320 CFUs on the same day.
- Mount Baker Beach: Sample A, 810; Sample B, 460
- Matthews Beach: Sample B, 830; Sample C, 570
“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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Other beaches remain open as temperatures climb into the 80s
The summer heat is expected to ramp back up this weekend into next week, reaching the low 80s in parts of the greater Seattle area. Options for cooling off at a local beach are limited, but not completely out of the picture.
Public Health noted that while a majority of beaches tested in the summers of 2020-2025 had good water quality at least 95% of the time, it is still recommended to check the Public Health beach bacteria map before spending a day at the beach.
Beaches that remain open for public use include Madrona Beach, Magnuson Beach, Meydenbauer Beach, and Luther Burbank Beach, among several others.
There is no information on how long the closures will be in effect.
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