Foss Reservoir
General data
- Name: Foss Reservoir
- Water system: Atchafalaya River
- Water type: River
- Progression: Washita River -> Lake Texoma -> Red River of the South -> Atchafalaya River -> Gulf of Mexico -> Atlantic Ocean -> Planet Earth
- Climates: Subtropical
- Continents: North America
- Countries: United States of America
Foss Reservoir, also known as Foss Lake, is in Custer County, Oklahoma on the Washita River, Oklahoma. The reservoir was constructed during 1958–1961 by the U. S. Bureau of Reclamation. The project was known originally as the Washita Basin Project. The lake and dam were named for the community of Foss, Oklahoma. Their primary purpose is to regulate flow of the river and to provide water for the cities of Bessie, Clinton, Cordell and Hobart. It is western Oklahoma's largest lake and lies entirely within Foss State Park. The reservoir has a surface area of 3,600 ha and a shoreline of 101 km. The capacity of the reservoir is 538,800,000 m3. The reservoir serves a catchment area of 3,870 km2. The reservoir has a mean depth of 7.0 m and a maximum depth of 27 m.