Posey Island State Park is a one-acre marine park in Washington’s San Juan Islands, occupying all of Posey Island on Spieden Channel near Roche Harbor and just north of Pearl Island. With about 1,000 feet of saltwater shoreline, it serves mainly as a camping stop for small watercraft. The island became a state park in 1960 through a lease from the U.S. Bureau of Land Management and is managed by the Washington State Parks and Recreation Commission. Its two campsites are part of the Cascadia Marine Trail and are reserved for visitors arriving by non-motorized watercraft.