Extensive areas of seasonally flooded river floodplain became permanently inundated shallow aquatic and wetland habitat, each with an impounded area above the lock and dam. For several decades following construction of the navigation dams, the UMR supported a wealth of fish, wildlife, and aquatic habitat. Unfortunately, habitat quality and the abundance of fish and wildlife has gradually been declining as the navigation pools age.
Most reservoirs initially have high levels of biological production.
Over time, reservoirs gradually fill with sediment, aquatic habitat quality declines, and they become less productive. This process has been occurring in the navigation pools of the Upper Mississippi River. The locks and dams created lake-like areas upstream from the structures and the river has been regulated for navigation with relatively stable water levels. Initially following dam construction, the navigation pools had a variety of water depths and numerous islands that supported a rich variety of fish and wildlife. Emergent and submersed aquatic vegetation flourished, providing food and cover for fish and wildlife.