Several beaches along Lake Washington, including Madison Park Beach and Matthews Beach in Seattle, were closed Tuesday due to high levels of bacteria.

Swim beaches in King County along Lake Washington and Lake Sammamish are tested every week between May and September for bacteria, which is an indicator of feces in the water. Some beaches are also tested for algal toxins, according to King County.

Check water quality of King County beaches using this interactive map

Public health officials say people and their pets should not swim or wade in these waters. Dogs are more likely to get sick since they drink more lake water than people, according to King County.

The following swim beaches around Lake Washington in Seattle, Renton and Bellevue are closed:

  • Gene Coulon in Renton
  • Newcastle Beach in Bellevue
  • Madison Park Beach in Seattle
  • Matthews Beach in Seattle

Closures are specific to a beach and King County says bacterial results can be different over short distances, so the quality in other parts of the lake is unknown.

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After a beach is closed, King County officials say they try to identify the source of the feces. Contaminated water can come from a variety of sources, including a sewage spill, dogs, geese, people and streams carrying feces from upstream areas.

In the past, closures have lasted a minimum of two to three weeks, though sometimes closures can last longer, said King County Department of Natural Resources and Parks ecologist Daniel Nidzgorski.

The water does not need to be treated, he said. Once the source of feces is identified and removed, the bacteria usually dissipates quickly, he said.

Tips on how to be a good steward the next time you’re at a swim beach:

  • Don’t feed waterfowl like ducks or geese. Food attracts them, which means more feces on the shore
  • Use a good swim diaper for babies and toddlers
  • Take a rinse before going into the water. Everyone has some feces on their bodies, Nidzgorski said. That can add up when thousands of people visit a popular beach each week
  • Leave your dog at home. Most swimming beaches also do not allow dogs

The Seattle Times is tracking water quality of King County beaches for the rest of the swimming season. To view the interactive map, visit st.news/KingCountyBeaches.