The Mobile River basin is the sixth largest basin in the Nation and the fourth largest in terms of streamflow. Flow in the Alabama and Tombigbee Rivers is generally regulated by upstream reservoirs, flood-control and navigational locks and dams, and hydroelectric plants. In 1985, the Tennessee-Tombigbee Waterway was opened. It joined the Tennessee and Tombigbee Rivers to provide a new trade route connecting Mobile and the Gulf Coast with the mid-section of the Nation. Reservoirs on the Alabama and Tombigbee Rivers and their tributaries are also used for drinking water and recreational activities such as fishing, swimming, and boating.
Fishing is one of the recreational uses of reservoirs in the Mobile River Basin.
Landforms in the Mobile River Basin study unit range from rugged mountains to coastal lowlands and are included in five physiographic provinces. The Blue Ridge and Piedmont, located in the northeast corner of the study unit, are characterized by igneous and metamorphic rocks and encompass 16 percent of the basin. To the east, the Valley and Ridge consists of a series of parallel ridges and valleys, all having a northeast trend. It is underlain by sandstone, shale, limestone, and dolomite rocks. The Valley and Ridge includes 16 percent of the basin.