sediment originating from both agricultural and urban sources. Pesti- 

 cides may not be having a direct effect on fishes in the Illinois River, 

 but pesticides in some fish from the Illinois exceed levels allowed by 

 the Food and Drug Administration (FDA) in fish for human consumption. 

 Industrial and municipal wastes 



Figure 4 shows the critically low dissolved oxygen levels in the 

 Illinois River during low flows in the summers of 1965 and 1966. Oxygen 

 levels were generally below saturation throughout the entire length of 

 the river; levels below 1.0 mg/1 occurred in Dresden, Peoria, and 

 LaGrange pools. 



Increases in dissolved oxygen are apparent below the navigation 

 dams (due to reaeration by the dams) and in lower Peoria Lake (perhaps 

 due to plankton, reduction of oxygen demand, and reaeration by turbulence 

 of the river) . The decreases in dissolved oxygen occur because organisms 

 living in the water, in the sediments, and attached to substrates (such 

 as rocks or navigation locks) utilize oxygen as they feed on organic 

 wastes (Butts, et al., 1975). 



The reduction in dissolved oxygen levels so far downstream of the 

 Chicago-Joliet and Peoria-Pekin metropolitan areas results from the 

 oxygen demand created as bacteria convert ammonia in sewage effluent to 

 nitrate. The rate at which populations of these nitrifying bacteria 

 develop is relatively slow, so that ammonia oxidation on the Upper 

 Illinois commences approximately three days time-of-travel below the 

 Lockport dam (mile 291.0): at mile 196 in the Peoria Pool during high 

 flows, and at mile 273 in the Dresden Pool during low flows (Butts, 

 et al., 1975). 



Ammonia places aquatic organisms in double jeopardy: it not only 

 causes a reduction in oxygen levels, it is also toxic. It is only the 

 un-ionized form of ammonia which is toxic, approximately 5 percent of 

 the total ammonia concentration in the Illinois River. Lubinski, et al. 

 (1974) reported that un-ionized ammonia concentrations in the Upper 

 Illinois River and Des Plaines River on occasion reached 40 to 60 per- 

 cent of a lethal level for bluegills. Un-ionized ammonia is more toxic 



