Authorized by Congress in the Flood control Act of 1938, and the Federal Water Pollution Control Act Amendments of 1961, John W. Flannagan Dam and Reservoir is a part of the Big Sandy flood protection system. The U.S. Army Corps of Engineers designed and supervised construction of the dam and now operates it for public benefits. Construction of the dam, spillway, and outlet works began in 1960, and was completed by 1964. The dam is 250 feet high and 916 feet long. The earth-filled dam is constructed of rock with a central clay core, which prevents water from passing through the dam. A 1,145-acre lake is formed behind the dam with almost 40 miles of shoreline.