Developing an inventory of coolwater streams for Illinois

In 2004 the Illinois Department of Natural Resources developed a list of candidate coolwater streams for management purposes. Since few temperature records were available coolwater stream segments were identified based on the presence of indicator fish species selected through consultation with Illinois fisheries biologists. This project aims to verify the thermal characteristics of candidate sites, determine the effectiveness of fish indicator species, and examine alternative methods for identifying coolwater reaches. We have monitored summer temperature in 153 reaches to describe the thermal conditions in Illinois streams. Thirty-one of these reaches have cold/cool temperature profiles (July mean < 22 oC). Thermal regimes of forty-two candidate sites have been described with only 45% demonstrating a coolwater condition. However, two-thirds of candidate sites that also contained high modeled potential ground water inputs (12/18) were coolwater. Most of the indicator fish species have been observed at sites covering a broad range of thermal conditions including 46% (6/13) in warmwater conditions. As an alternative to using indicator species water temperature data have been used to develop state-wide thermal models to predict conditions in streams. Temperature models appear to predict state-wide thermal conditions at least as well as the presence of indicator fish species.