(Table 1). Twenty-four of the sites were along the Illinois River, with two additional 

 sites on the lower Des Plaines River, which along with the Illinois River is part of the 

 Illinois Waterway. One additional site was on the Mississippi River (Figure 1). 

 Seventeen of the sites were in side channels; the rest of the sites were in other 

 habitats, including the main channel border, or in a combination of habitat types (see 

 Lerczak et al. 1994:9). By calculating the average river mile of each fish sampling 

 site for the total period of record (1957-present), the sites were "renamed" in 1998 to 

 reflect river mile (Figure 1). For this and all subsequent reports, we will refer to sites 

 by these approximate average river miles (site mile. Tables 1-5) for use in all figures 

 and tables. In text we will refer to sites by average river mile as well as by common 

 site descriptions (e.g., Brickhouse Slough, Mortland Island, etc.). 



MATERIALS AND METHODS 



Fish populations were sampled by electrofishing from a 16-ft (5-m) aluminum 

 boat using a Homelite 3000-watt, three-phase AC electric generator. Boat 

 configuration includes three poles extended from the bow with metal electrodes, 

 connecting to the electric generator, extended from the ends of the poles to 

 approximately 20 inches (0.5 m) below the water line. The same generator and 

 electrode configuration have been used since 1957. 



Prior to fish sampling, water quality and flow measurements (e.g., dissolved 



