To maintain a 9-foot-deep channel on the Upper Mississippi , the US Army Corps of Engineers built a series of locks and dams on the river in the 1930s. Ten such locks and dams control water flow along Wisconsin 's portion of the Great River Road .

The dams create pools behind them allowing the river to “step-down” as it flows south. The locks are water elevators that move boats up or down between pools. Using a lock is called “locking through.” Locking through is free – on a first-come, first-served basis. The procedure for locking through is broadcast on Marine Band Channel 14.

Strong currents can exist above and below locks and dams – stay out of these restricted areas. Wing dams are long piles of rock placed in the river to direct the channel. In high water, they can be submerged just below the surface. Avoid areas of rough water that may indicate a submerged wing dam.

The 9-foot main channel is marked in the river by buoys or “day marks.” When traveling upstream, green buoys mark the left edge of the channel; red buoys mark the right edge.