Comparative fish assemblages of the Lake Decatur watershed

Diminished water quality and availability, closure of fisheries, extirpation of species, groundwater depletion, and more frequent and intense flooding are increasingly distinguished as consequences of current river management associated with .impoundments The Sangamon River Basin is a 14,000 km2 watershed covering all or portions of eighteen counties in east central Illinois. Although there are major metropolitan areas within the basin, agriculture comprises more than 80% of current land use. More than 3540 km of streams within the basin course through glacial and alluvial deposits creating typically low gradient stream with sand and gravel substrates, but they have been impacted for most of the past century, receiving inputs from both point and non-point sources. I found differences between fish assemblages and fish-based indices of biotic integrity in eight tributaries to the Sangamon River above of Lake Decatur and those in the river mainstem downstream of the reservoir. These changes in fish assemblages likely are the result of altered physical habitat and chemical water quality.