Alabama's Cahaba River
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 turns southeast and joins the Alabama River 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 stretches from the Appalachian Plateau to the Coastal Plain of Alabama. The Mobile River basin has the largest Gulf Coast drainage basin east of the Mississippi River, and the Cahaba is one of seven river systems that contributes to its flow. The terrestrial biome of the river is classified as Eastern Deciduous Forest.
The region of Alabama where the Cahaba River begins was formed in the Paleozoic era. The valley soils consist of gravel, sand, and clay, while the ridges consist of chert and sandstone. The upper Cahaba region contains gravel, clay, and sand, while in the lower Cahaba region, the soils are calcareous, or chalky.
The waters of the Cahaba are home to more than 131 species of freshwater fishes — 18 of which have been found in no other river system — 40 species of mussels, and 35 species of snails. 69 of these species are endangered.
The endemic freshwater snail, Elimia cahawbensis, is named after the river. One species long thought to be extinct, the Oblong rocksnail Leptoxis compacta, was rediscovered in the Cahaba in 2011.
Due to damming, pollution, transportation, and erosion, the Cahaba has suffered losses of species. Almost a quarter of the original documented mussel species in the Cahaba have disappeared, with similar trends in the fish and snail numbers. Still, many species have still been discovered and rediscovered in the surrounding region. This region is most noted for containing numerous species of mollusks and snails, including 13 snail species not found anywhere else in the world. These species feed other aquatic dwelling animals, improve water quality by eating algae, and even indicate environmental issues due to their receptiveness of pollution.
The Cahaba flows through heavily populated areas in the Birmingham metropolitan area. It serves as the source of drinking water in the upper course for over 1 million people, and is also a popular recreation destination.