Utilization of backwater habitats by unionid mussels Tucker, J. K., C. H. Theiling, and J. B. Camerer. 1996. Utilization of backwater habitats by unionid mussels (Bivalvia: Unionidae) on the lower Illinois River and in Pool 26 of the Upper Mississippi River. Transactions of the Illinois State Academy of Science 89(1 and 2):113 122. Reprinted by U.S. Geological Survey, Environmental Management Technical Center, Onalaska, Wisconsin, September 1997. LTRMP 97-R019. 10 pp. (NTIS #PB98-104250) ABSTRACT Samples of the unionid faunas from two contiguous and five isolated backwaters of the lower Illinois River and Pool 26 of the Upper Mississippi River revealed differences in species composition between the two habitat types. Contiguous backwaters supported diverse faunas (7 to 14 species) near their connections with the river, whereas isolated backwaters supported only three or four species. Species diversity decreased within contiguous backwaters suggesting that the river-backwater interaction is important in maintaining unionid species diversity in these habitats. The common practice of isolating backwaters from the river using levees to prevent siltation may lead to reduced unionid diversity. KEYWORDS Effects of impoundment, habitat utilization, Illinois River, Mississippi River, species diversity in backwater lakes, Unionidae