Edited from Wikipedia:
Hoover Dam, in Blendon Township, near Westerville, Ohio, dams the Big Walnut Creek to form the Hoover Memorial Reservoir. This reservoir is a major water source for the city of Columbus, Ohio. It holds 20.8 billion gallons of water and has a surface area of 3,272 acres, or about five square miles. The dam was dedicated in 1955. It was named for two brothers, Charles P. Hoover and Clarence B. Hoover, to honor their careers with the City of Columbus Waterworks.