to aquatic organisms when dissolved oxygen levels are low than when 

 oxygen levels are high. The combination of low dissolved oxygen and 

 high un-ionized ammonia levels in the Upper Illinois River is probably 

 stressful to fish. 



Low dissolved oxygen levels are also partially attributable to oxy- 

 gen utilization by microorganisms, tubificid worms, and midge larvae 

 living in sediment deposits on the bottom of river. Sediments in many 

 parts of the river are high in organic content and resemble primary 

 sewage sludge (Butts, 1974; Butts, et al . , 1975). 



Stormwater probably contributes considerable oxygen-demanding waste 

 and sediment to the river. This waste is washed from streets, gutters, 

 parking lots, etc., during storms. In addition, stormwater overloads 

 sewage systems, so that raw sewage mixed with stormwater is discharged 

 directly to the river. The lowest dissolved oxygen levels (1.1 mg/1) 

 observed in the Upper Illinois River during a 1971-1972 study by the 

 Illinois Water Survey occurred in Peoria Pool while water levels were 

 rising to a flood crest (Butts, et al . , 1975). During persistently high 

 flows, the oxygen levels recover, because streets, gutters, and sewers 

 are swept clean by the initial rainfall and there is a dilution effect. 



Industrial effluents presently enter the river directly, or in- 

 directly, through municipal sewage systems. Domestic wastes contain 

 materials such as LAS detergents and fluoride (added to drinking water) , 

 which can be toxic to aquatic organisms at certain concentrations. 



Lubinski, et al . (1974) expressed the concentrations of individual 

 toxicants in the Illinois River as fractions of the lethal concentra- 

 tions (96-hr LC50's) to bluegills. To do this, Lubinski, et al. (1974) 

 used chemical monitoring data, gathered by the Illinois Environmental 

 Protection Agency (EPA) , for 17 stations on the Illinois River and bio- 

 assay information available in the literature or from their (Lubinski, 

 et al.) own experiments. They used the bluegill as a reference organism 

 because it is found in the Illinois River and a great deal of informa- 

 tion is available on the toxicity of chemicals to bluegills. Certain 

 assumptions and calculations were made (as detailed in Lubinski, et al., 



