It was named after Congressman John Williams Flannagan, Jr.[1] 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 262-foot (80 m)-high intake structure is located north of the dam, and contains 8-by-4-foot (2.4 by 1.2 m) gates which control the amount of water released into Russell Fork River.

[2] Built primarily for flood control, the lake surface is kept at an elevation of 1,396 feet (426 m) above sea level for recreation during the summer.

The water, which runs off from the 221-square-mile (570 km2) drainage basin behind the dam, is stored in the reservoir to protect life and property downstream.

Some of the most challenging rapids in the eastern U.S. can be found while traveling through Breaks Interstate Park with names like 20 Stitches, Broken Nose and Triple Drop.