The Cahaba River is the longest free-flowing river in Alabama and is among the most scenic and biologically diverse rivers in the United States. The Cahaba River is a major tributary of the Alabama River and part of the larger Mobile River basin. With headwaters near Birmingham, the Cahaba meanders to the southwest, then at Heiberger turns southeast and joins the Alabama River at the ghost town and former Alabama capital of Cahaba in Dallas County. Contained entirely within central Alabama, the Cahaba River is 194 miles long and drains an area of 1,870 square miles.
The Cahaba River begins in the Valley and Ridge region bounded by the Piedmont to the southeast and the Cumberland Plateau to the northwest. It has two major physical regions: Upper and Lower Cahaba. The river empties into the Alabama River. The upper Cahaba is approximately the first 100 miles that starts at the headwaters and continues to the fall line, a region in which the Appalachian Mountains end and the Gulf Coastal Plain begins. It passes through Trussville, Leeds, Irondale, Birmingham, Mountain Brook, Helena, West Blocton, and Centerville. The lower Cahaba begins at the fall line and continues through Selma and empties into the Alabama River at the former town of Cahaba.