The upstream portions of many pools are similar to the unimpounded river, whereas the downstream reaches are similar to reservoirs. The Upper Mississippi contains a diverse array of wetland, open-water, and floodplain habitats, including extensive national wildlife and fish refuges.
Pollutants also enter the river from point sources.
We examine recent temporal trends in the abundance of several key groups of organisms in the Upper Mississippi River and show that certain flora and fauna have declined along substantial reaches of the river. Information on the abundance of selected riverine biota was obtained by compiling historical data and by censusing or sampling. Bottom-dwelling invertebrates, collectively termed benthic macroinvertebrates, were extensively studied. Some of these organisms are important in the diets of fish and wildlife and are useful as biological indicators of toxic pollution. Wilson et al.