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 US gallons of water and has a surface area of 3,272 acres, or about five square miles. Construction began during 1953 due to the increased water demand of post-war Columbus. The project was completed and dedicated in 1955 and the dam officially opened in 1958.