The change in the composition of the small bottom- 

 fauna, in turn, includes the disappearance since 

 1915 of five out of seven families of snails; of 

 more than half a dozen species of bottom-dwelling 

 larval midges; and of twelve out of thirteen or 

 fourteen families of "other insects," worms, small 

 Crustacea, and other small bottom-invertebrates." 



Richardson (1921b) estimated that the midsummer standing crop of 

 bottom and weed fauna had been reduced by a total of 34,500,000 lbs 

 in the additional 103-mile section of the Illinois River affected by 

 Chicago effluents between 1915 and 1920. He estimated that this 

 drastic reduction in food organisms represented a loss of about 

 7,000,000 lbs of potential fish-yield. 

 Leveeing and draining (1903-1926) 



One of the major impacts on the Illinois River below Hennepin was 

 the leveeing and draining of bottomland areas, primarily in the period 

 1903-1926. Of 400,000 bottomland acres subject to overflow by the 

 river, approximately 200,000 are now behind levees with a consequent 

 reduction in wildlife and fish habitat (Mills et al., 1966). The back- 

 waters and bottomland lakes of the Illinois River were, and are, criti- 

 cally important to fish and wildlife production. Richardson (1921a) 

 reported that the largest poundages of fish per acre were taken in 

 reaches of the river where the largest quotas of connecting lake acreage 

 existed: 



"Taking the year 1908 as an illustration, and using 

 the figures for separate shipping points obtained by the 

 Illinois Fish Commission in that year, we find for the 

 59.3 miles of river and lakes between Copperas Creek dam 

 (river mile 136.9) and LaGrange dam (River mile 77.6), 

 with about 90% of its acreage consisting of lakes and ponds, 

 an average fish-yield per acre for water levels prevailing 

 half the year, of 178.4 pounds; for the 87 miles from LaSalle 

 (river mile 223.9) to Copperas Creek dam, with about 83% lakes, 

 130.4 pounds; and for the lower 77 miles, LaGrange to Grafton, 

 with around 63% lakes, only 69.8 pounds." 



Richardson indicates that well over 80 percent of the total fish yield 

 came from the lakes and that much less than 20 percent came from the 



