A cooperative survey of the aquatic resources of the DuPage River basin was conducted in 1983. Fish, macroinvertebrate, water, sediment, and habitat data were collected as part of the survey. Twenty-one stations were established within the West Branch of the DuPage River, East Branch of the DuPage River, Lily Cache Creek, and the mainstem of the DuPage River. Environmental quality was summarized utilizing various indices, including the Water Quality Index (WQI), Macroinvertebrate Biotic Index (MBI), Index of Biotic Integrity (AIBI) and, to a limited extent, habitat (PIBI). Individual stations were evaluated for degree of aquatic life use support and classified according to the biological stream classification (BSC) system used for rating Illinois streams.