The authors compiled distributional and ecological information on the class Rotifera from both flood controlled and uncontrolled reaches of the Atchafalya River Basin, a large river-swamp in the south-central United States. In the minimally altered lower basin a variety of aquatic habitats within a small area resulted in a very diverse rotifer community consisting of an average of 46 taxa. In contrast, only an average of 28 different taxa were collected in leeved upper basin habitats. As a result of cluster analysis it was possible to identify rotifer communities associated with areas of similar water quality. Variations in suspended solids, total dissolved solids, and organic carbon were most often significantly associated with variations in rotifer numbers from the lower basin. Seasonal flushing of backwater areas by mainstem waters is very important in maintaining the diversity of these lower basin rotifer communities.