Lake Sammamish State Park is the closest big freshwater beach to Seattle, 512 acres at the south end of the lake where Issaquah Creek comes in, right off I-90 at exit 15. It has two swimming beaches. Sunset Beach is the larger one, with a long sand shore, a bathhouse, a cafe that runs weekends in May and September and daily from mid-June to Labor Day, and the park's new playground. Tibbetts Beach is smaller and quieter, a few hundred yards east past the picnic shelters, and it is where Lake Sammamish Paddle Co. rents kayaks, paddleboards and pedal boats from Memorial Day to Labor Day and on fall weekends. Both beaches have buoyed swim areas, picnic tables and grills. There have been no lifeguards since the park's 40-year lifeguard program ended in the 1990s; a two-year pilot brought them back briefly and they were gone again after 2010.

The lake is 7 miles long and up to 105 feet deep, and it warms slowly: 50 to 55 degrees in winter and 70 to 75 by late summer. King County samples bacteria at both beaches weekly from mid-May to late September and posts the results, and the park page links to the current numbers. Dogs are allowed on leash in the park but not in the swim areas.

Parking needs a Discover Pass, $10 a day or $45 a year, from the pay stations; the watercraft launch fee is $7. The park is open 6:30 a.m. to dusk year round and is day use only, though the Hans Jensen group camp east of the boat launch can be reserved. Paved and gravel trails connect the beaches to the wetlands along Issaquah Creek, where great blue herons nest in a rookery and bald eagles work the creek mouth, and the park has seven full-size soccer fields, two softball fields, volleyball courts and four reservable shelters. Outdoors for All lends adaptive bikes free from the Sunset Beach bathhouse, May through September. As of 2026 the footbridges over Issaquah Creek and Tibbetts Creek are closed for erosion repairs, which cuts the walking loop between the beach side and the boat launch side.

The land was dairy farms until the state bought the first 210 acres in 1950, and Issaquah had been swimming here for decades before that. Sunset Beach was the only beach for years and half its current size; Tibbetts Beach came with a 1965 land purchase. The park's crowds in the 1970s and 80s were legendary, with 35,000 people on a hot weekend day, and the Friends of Lake Sammamish State Park, formed in 2013, has been behind the recent playground and shelter upgrades. The address is 2182 NW Sammamish Road, Issaquah; the park office is 425-455-7010.