To achieve a 9-foot channel in the Upper Mississippi River, the construction of a system of navigation locks and dams was authorized in 1930. Dams are built on rivers to hold back water and form deeper navigation "pools." Most pools in the United States are maintained at a constant minimum water depth of 9 feet for safe navigation. Dams allow river vessels to use a series of locks to "step" up or down the river from one water level to another.
The Corps operates the locks and dams on the Mississippi River for navigation, not flood control. The locks and dams create slack-water pools for navigation during periods of low- and moderate-level water. For each pool, there is a primary control point, where a predetermined water elevation must be kept for navigation to continue.
The St. Paul District operates and maintains 13 locks and dams beginning at Upper St. Anthony Falls in downtown Minneapolis and ending at Lock and Dam 10 in Guttenberg, Iowa.
For recreational craft to pass through a lock and dam, there is a specific locking procedure. It's a fun and unique experience. Interpretive materials and brochures are available at all locks.