Skip to main content
King County logo


Natural Resources and Parks
Public Affairs

King County’s weekly swim beach water quality testing helps protect swimmers’ health all summer long


The King County Swimming Beach Monitoring Program is underway to test water quality at the most popular lake beaches countywide. Free alerts are available to help residents keep their families and pets safe. Sign up at


Towels, sunscreen and snacks aren’t the only items that should be on your checklist when getting ready to head to the beach. Checking to make sure that your favorite beach is open for swimming and water recreation is another easy way to help protect your family and ensure having fun.

King County takes water samples at 28 lake swimming beaches every week throughout the summertime swim season, including popular spots like Green Lake, as well as Juanita Beach and Magnuson Park on Lake Washington.  

Signing up for King County’s beach alerts provides weekly updates to let people know if any of the county’s most visited freshwater swimming beaches are exceeding thresholds for either bacteria or algal toxins in the water. People can sign up to receive a weekly status update – or just alerts when a beach is closed – at

Swimming beaches in this monitoring program are tested for bacteria every week throughout the summer. Some beaches are also tested for algal toxins every week, while other beaches are tested only if there is a visible algal bloom. If a beach is closed due to high concentrations of either bacteria or algal toxins in the water, closure signs will be posted at the beach and will be posted on the Swim Beach Monitoring program website. 

Fecal bacteria can make people sick and when the concentrations exceed the thresholds, that’s when Public Health – Seattle & King County makes the determination that a beach should be closed to water recreation to protect public health.

Here are four simple ways to help limit bacteria entering the water: 

 Only take your dog to a designated dog beach.

• Don’t feed geese and other birds at the beach. The more they hang out at the beach or on a dock, the more poop gets washed into the water.

 Use swim diapers for babies and toddlers.

 Wash off before entering the water.

Marine beaches such as Golden Gardens, Alki Beach or Seahurst Park are monitored through the Washington State Department of Ecology BEACH program.

King County Swim Beach Monitoring program
Washington State Department of Ecology saltwater beach monitoring