Rivers are dammed to form impoundments for many reasons, including: transportation, hydroelectric power, water supply, flood control, and reacreation. The rivers of Alabama have been altered dramatically by dams, primarily for transportation and hydropower. This is important to freshwater studies because of its consequences for biota. The environmental effects of dams include habitat loss & modification, downstream effects—discharge pattern and temperature pattern, water chemistry, channel formation, and upstream & downstream effects on migration and dispersal of biota.
In Alabama, the Alabama Power company was originally started for its hydropower purposes. The image included in this post is an example of the turbine propellers used in dams in Alabama that generate electricity. This is one I saw on a field trip to Hold Dam located in Tuscaloosa.