Intensive agricultural land use dominates Iowa's landscape, leading to degradation of the environmental quality of Iowa's land, water, and biota. This study was designed to determine how land use practices affect stream environments in a typical Iowa agricultural landscape. Thirteen first order streams and their watersheds within the Northwest Iowa landform region were studied. Corn and soybeans are grown on the flat headlands of this area, while the steeper terrain is wooded or pastured. Steep erosional topography occurs in association with the Little Sioux River valley. Watershed areas ranged from 72 to 1030 hectares. Geographic Information Systems analysis was employed to categorize land use within each watershed, including that of riparian areas. Instream physical features were measured on five occasions in 1994, and stream water quality was assessed from biweekly water collections made March through October 1994, and March through September 1995.;Benthic macroinvertebrate sampling occur-red in June, August, and September 1994. Principal components analysis was used to place watersheds and streams in groups according to land use. Most watershed variation was explained by area, topography, and riparian conditions. Strong relationships existed between agricultural land use in the riparian zone, instream physical features, and water quality. From these relationships, four groups of watersheds were identified from land use patterns in the riparian zone. These groups were used to describe differences in instream physical features, water quality, and macroinvertebrate community structure. The least disturbed streams according to land use, channel morphology, and water quality possessed a high quality, but low quantity, macroinvertebrate community.;Streams with seemingly lower quality habitat, but more habitat available due to greater stream width and discharge, supported a more abundant and diverse macroinvertebrate assemblage than streams with less total but higher quality, habitat. Riparian management in these watersheds seems to be important in determining stream environmental quality based upon physical and chemical characteristics, while the amount and quality of instream physical habitat is most important in determining macroinvertebrate community structure in these headwater streams.