Multivariate analyses of fish-community, water- quality, streambed-sediment-quality, and habitat data collected from 1982 through 1984 in the Fox, Des Plaines, and Du Page River Basins in northeastern Illinois indicate that fish-community structure was strongly related to water-quality gradients commonly associated with differences between agricultural and urban land uses. Detrended correspondence analysis (DCA) and the Alternate Index of Biotic Integrity (AIBI) tended to group fish communities by river basin. Streams in the predominantly agricultural Fox River Basin tended to have similar DCA scores, the highest AIBI scores, and relatively diverse fish communities that usually included several intolerant species. Streams in the more heavily urbanized Chicago, Little Calumet, Des Plaines, and Du Page River Basins tended to have lower AIBI scores and fish communities dominated by fewer; more tolerant species. Correlative (Spearman's rho) and graphical analyses showed that DCA and AIBI scores for nonwadable sites were more strongly related to water qualiity and streambed- sediment quality than to habitat conditions. DCA and AIBI scores for wadable sites were most strongly related to water quality, were not related to streambed-sediment quality, and were moderately related to habitat variables indicative of stream size. Streams in the Fox River Basin had the smallest concentrations of chemical constituents commonly associated with anthropogenic sources. Streams in the heavily urbanized Des Plaines and Du Page River Basins had larger concentrations of chemical constituents associated with urban runoff and point-sourca discharges. Although fish-community structure was strongly related to the water quality, U.S. Environmental Protection Agency acute and chronic criteria for the protection of freshwater aquatic life were exceeded at few stations. These fish communities may have been responding either to concentrations below the U.S. Environmental Protection Agency criteria or to cumulative or synergistic effects of overall water quality.