Clarke Beach Park is a 9-acre waterfront park run by the City of Mercer Island Parks and Recreation Department on the southeast shore of Mercer Island, facing the main body of Lake Washington toward Newcastle and Renton. The land was a Girl Scout camp (Camp Tarywood) before the city bought it in 1969 and 1970 with Washington State marine recreation money, and it opened as a park in 1971. It carries the name of Mabel Clarke, an island pioneer who arrived from Iowa around 1906. Of all the public beaches on the island, Clarke has the longest stretch of shoreline, yet it is usually the quietest of them.

The entrance is on East Mercer Way at SE 77th Place, about 4 km south of Mercer Island's town center. From I-90, take Island Crest Way or East Mercer Way south. Parking is free in a small paved lot by the road, with two accessible stalls. From the lot, a paved path drops steeply through the woods to the lawn and the water, so plan on a short but stiff climb back up with your gear. There is no entry fee, and the park is open to everyone, not just island residents. City parks on Mercer Island are open daily from 6:00 AM to 10:00 PM.

The swim area sits on the shoreline below the lawn, enclosed by a buoy line and framed by the park's two piers, one used for swimming and one for fishing. Much of the waterfront is an old concrete bulkhead with steps leading down into the lake, plus a small patch of sand, so this is more of a lawn-and-dock spot than a sandy beach. Lake Washington is still fresh water with no real current; the surface is warmest, around 70 F, in late July and August, and deeper water stays cold. Clarke Beach is not staffed by lifeguards at any time of year, and the city's posted rule is swim at your own risk. Because the park faces east, the beach drops into shade earlier in the afternoon than the island's west-side parks.

Keep inside the buoys. Lake Washington carries heavy summer boat traffic, and the Mercer Island Police Marine Patrol works the waters around the island. Clarke Beach is not one of the Mercer Island beaches that King County samples weekly for bacteria during the summer swim season (only Luther Burbank and Groveland are), so after heavy rain or if you see scum or discolored water, it's safer to stay out. Dogs and other pets are banned from the public swim areas from May 1 through September 30; the rest of the year they are allowed on the beach on a leash.

Facilities include restrooms that are open in summer, a drinking fountain, picnic tables, a grass lawn and a short forested loop trail of about a third of a mile that the volunteer forest stewards have been replanting with native trees and shrubs. The city lists the park as certified wildlife habitat and a restoration area. The city is also working on a joint infrastructure plan for Clarke and nearby Groveland Beach. The preferred design for Clarke would replace the concrete bulkheads with gradual beach transitions using a gravel mix, logs and boulders for fish habitat, and would rebuild both existing piers in their current layout. The city's project page says plan review with the Parks and Recreation Commission and City Council is on hold, and no construction dates have been announced, so the beach is open in its current form.