The macroinvertebrate community of the Mississippi River near Monticell, Minnesota, was examined for 22 months. Quantitative bottom fauna information was obtained by use of concrete block artificial substrate sampling units. Representative organisms were obtained from seven (7) orders, 15 families and 35 genera of benthic macroinvertebrates. All taxa collected displayed definite seasonal trends. The Orders Trichoptera, Diptera, and Ephemeroptera were the most abundant groups collected, Trichoptera (Hydropsyche and Cheumatopsyche) were the dominant members of the benthic population in both numbers and biomass. Midges and blackflies were the dominant Diptera. Pseudocloeon, Stenonema, and Ephemerella were the most frequently collected mayflies
