Matthews Beach Park is a 22-acre city park on the west shore of Lake Washington in northeast Seattle, and Seattle Parks and Recreation calls the beach here the city's largest freshwater bathing beach. The address is 5100 NE 93rd Street, in the Matthews Beach neighborhood. The park is open 6 a.m. to 10 p.m. There is no admission charge and no charge to swim.

Swimming happens inside a roped area off a sand and gravel shore. Seattle Parks maintains the bottom inside the ropes, keeps it clear of aquatic weeds, and keeps boat traffic out, which is why lifeguards discourage swimming just past the perimeter. A floating platform is anchored offshore with a 1-meter and a 3-meter diving board. The 3-meter board depends on water depth and in most years comes down before the season ends. Children have to pass a lifeguard-administered swim test before going outside the ropes.

Lifeguards worked the beach from June 27 to September 7 in 2026, one of nine lifeguarded beaches the city runs on Lake Washington and Green Lake. Matthews Beach is one of the few that stays staffed through the late-season window of August 24 to September 7, when several other city beaches close for the year. Free swim lessons for ages 6 to 16 run in two-week sessions through the summer. Outside the guarded season the park stays open, and Seattle Parks hosts a Polar Bear Plunge here on New Year's Day.

Check the water before you drive out. King County samples roughly 30 lake swim beaches weekly from mid-May to mid-September, testing for E. coli and, at many beaches, toxic algae, and Public Health Seattle and King County reads the results and calls closures. Matthews Beach closes more often than most. In August 2026 two samples came back at 35,000 and 27,000 colony forming units per 100 milliliters against a 320 CFU threshold, the highest readings at this beach since 2019. It closed on August 11 and reopened on August 19. The county attributes most summer closures at its lake beaches to waterfowl droppings rather than sewage, and asks people not to feed the birds.

Thornton Creek empties into the lake at the south end of the park. The park takes its name from John G. Matthews, who homesteaded here in the 1880s, and long before that the shoreline near the creek mouth held a Duwamish village. Seattle bought the first ten acres in 1951. In the 1940s the ground just south of the main beach held Pan American World Airways offices and the dock for its Clipper flying boats. The Burke-Gilman Trail runs along the back of the park on the old Northern Pacific and Burlington Northern rail grade, and the curve of the trail still traces the outline of the original cove. This park is where that trail first got public momentum. Neighborhood organizers staged a hike-in here in 1971 that drew more than 2,000 people, and the first 12.1 miles were dedicated at Matthews Beach Park on August 19, 1978.