When a boat enters the lock, the gates close and the water level inside is raised to the upstream level or lowered to the downstream level, depending on which way the boat is moving. The locks are filled and emptied by gravity, with no pumps used. The navigation of the Arkansas River was the largest Corps of Engineers public works project at the time of its completion in 1971, costing $1.2 billion. It was named for the US Senators who sponsored the appropriation bill, McClellan of Arkansas and Kerr of Oklahoma. The project addressed navigation, flood control, hydroelectric power generation, bank stabilization, recreational opportunities, and environmental issues. The navigation channel is 445 miles long, beginning at the Arkansas Post Canal, which connects to the White and Mississippi Rivers.