Pike Island, two locks and a gated dam, one of the two major types of dams in service. Controls the water level in the navigation pool upriver of the dam. Machinery moves large chains which lift gates that are hinged into the body of the piers. The gates are raised or lowered to control the amount of water flowing under them. The upstream pool is maintained at a relatively constant level for an authorized depth of at least 9 feet throughout its length. The dam cannot be operated to control flood flows.