inventory of the lower portion of the Illinois River, undertaken by the 

 St. Louis District, U. S. Army Corps of Engineers. 



The Study Area 



The Illinois River begins at the confluence of the Des Plaines and 

 Kankakee Rivers. Navigational locks and dams along the rivers impound 

 waters, called pools, which provide convenient reference to the geo- 

 graphic location of various sections of the study area (see Figures 1 

 and 2). 



The lower part of the Illinois, the area of principal interest in 

 this study, is influenced by the Alton Dam on the Mississippi. In the 

 middle portion are the pools formed by the LaGrange Dam and the Peoria 

 Dam. Pools sampled in the upper portion are, in upstream order, Starved 

 Rock, Marseilles, and Dresden. The Dresden Dam is located 1.4 miles from 

 the rivers' confluence and the Dresden Pool actually extends into the 

 Des Plaines and Kankakee Rivers. The one sampling station in the Dresden 

 Pool is located in the Des Plaines River. 



The Illinois River, the Des Plaines River, the Chicago Sanitary and 

 Ship Canal, and the Chicago River form the Illinois Waterway, which pro- 

 vides a navigation channel 9 ft deep and 160-300 ft wide, connecting the 

 Mississippi River and Lake Michigan. Charts of the Illinois Waterway 

 have been prepared by the U. S. Army Engineer District, Chicago (1970) 

 and locations are given in river miles, starting from mile 0.0 at the 

 confluence of the Illinois and Mississippi Rivers, at Grafton, Illinois, 

 and proceeding upstream to Chicago. Along the river itself, mileages 

 are often given on navigation aids such as buoys, markers, and lights. 

 River mileages provide an accurate means of locating sites along the 

 Illinois Waterway, and are used throughout the text. 



The Des Plaines River receives municipal and industrial effluents 

 from the Chicago area, while the Kankakee is relatively unpolluted. The 

 Des Plaines also contributes more to the total flow of the Upper 

 Illinois River than the Kankakee. During the lowest flows expected for 



