Foss Reservoir, Water reservoir in Custer County, Oklahoma.

Foss Reservoir is a reservoir on the Washita River in Custer County, Oklahoma, about 15 miles west of Clinton. It covers 8,800 acres, has 63 miles of shoreline, a mean depth of 23 feet and a maximum depth of 89 feet. It is held back by Foss Dam, which is 142 feet high and 18,130 feet long. The reservoir lies entirely within Foss State Park.

Foss Dam was begun in October 1958 and the reservoir filled between 1958 and 1961, built by the U.S. Bureau of Reclamation as the Washita Basin Project on the Washita River. The lake and dam take their name from the community of Foss, about 6 miles south of the site. The dam is 142 feet high and 18,130 feet long.

The lake and dam take their name from the community of Foss, about 6 miles south of the site. The reservoir lies entirely within Foss State Park, which holds 8 campgrounds, a swimming beach, 6 boat ramps and 19 miles of equestrian and multi-use trails. A herd of bison once kept in the park was sold by the state as surplus property.

The location has several boat ramps and fishing docks, including covered and lighted facilities near developed areas. Campsites with hookups are available if you plan to stay longer and want basic services.

In September 2013, Oklahoma Highway Patrol officers testing sonar found two cars on the lake bed: a 1952 Chevrolet and a 1969 Chevrolet Camaro, each holding three sets of skeletal remains. The cases, open since 1969 and 1970, were ruled accidental in October 2014.