a 7-day period at a recurrence interval of 10 years, the Illinois State 

 Water Survey (Singh and Stall, 1973) calculated that the Des Plaines 

 and Kankakee would contribute 1926 and 455 cfs of water, respectively, 

 to the Illinois. 



Approximately 93 percent by volume of all waste flowing to the 

 upper portion of the Illinois Waterway (mile 179.0 at Chillicothe to 

 mile 292.1 at Lockport) , including all of the Upper Illinois River, 

 originates from three treatment plants of the Metropolitan Sanitary 

 District of Greater Chicago (Butts, et al., 1975). As a consequence, 

 thick oxygen consuming sludge and sediment deposits exist in the 

 Dresden and Starved Rock Pools, and a portion of the Peoria Pool; there 

 is a significant carbonaceous oxygen demand exerted in the Dresden Pool; 

 and a significant nitrogenous oxygen demand exerted in much of the 

 Illinois River (Butts, et al. , 1975; Butts, et al., 1970). These de- 

 mands cause low oxygen levels to occur in much of the Illinois River 

 during summer low-flow periods, with the upper and middle sections more 

 severely affected than the lower section. Thermal effluents in the 

 vicinity of Joliet (mile 284.0) raise the whole temperature profile of 

 the Des Plaines and Upper Illinois Rivers downstream to miles 200-180 

 (Butts, et al. , 1975). 



The upper section of the Illinois River may also be differentiated 

 from the other two sections by its lower turbidity. Turbidity is less 

 there because above Hennepin (mile 207.5) the river bottom is generally 

 rocky, although in some sections the rock is overlain with sediment. 

 In contrast, the Alton, LaGrange, and Peoria Pools are more turbid be- 

 cause of soft mud bottoms and heavy silt loads from tributary streams 

 that have drained agricultural areas. These muds are kept in suspension 

 by current and wave action produced by wind, towboats , and pleasure 

 craft. 



For fish and wildlife, the most productive portions of the Illinois 

 are the middle and lower sections below Hennepin. Here, the river flows 

 through a large, late Pleistocene valley: lateral levee lakes, side 

 channels, backwaters, and marshes fill the valley and provide an excel- 

 lent habitat for fish and wildlife. 



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