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 (79,000,000 m3) of water and has a surface area of 3,272 acres (13.24 km2), or about five square miles.