river itself (Richardson, 1921a) . The bottomland lakes supported an 

 abundant aquatic weed-inhabiting invertebrate fauna, which supplied 

 food for sunfish, crappie, largemouth bass, northern pike, and yellow 

 perch. 



Two important conclusions can be drawn from Richardson's work 

 (1921a) regarding the bottom fauna and fish production in the lower 

 80 miles of the Illinois River. First, this section of the river channel 

 had a less abundant bottom fauna than the section immediately upstream 

 because of a lack of soft mud substrate (Richardson, 1921a) relatively 

 more frequent dredging operations for channel maintenance (Richardson, 

 1921a), and because the absence of backwater areas (as a result of 

 leveeing) concentrated the feeding activities of the annual upstream 

 runs of large carp and buffalo in the spring (Richardson, 1921a). 

 Second, as a result of more extensive levees along the lower 80 miles 

 of river, there was a paucity of the connecting lake acreage necessary 

 to support an abundant weed fauna and consequently, a high level of 

 fish production was not possible. 

 High navigation dams (1930 's) 



In the 1930' s, high navigation dams were constructed at Dresden 

 Heights (22 ft), Marseilles (24 ft), Starved Rock (19 ft), Peoria 

 (11 ft), and LaGrange (10 ft). The navigation dam on the Mississippi 

 at Alton raised water levels in the Illinois River as far north as 

 Hardin, mile 21.0 (Mills, et al., 1966). Timber and brush were cleared 

 from areas due to be inundated by the new dams. Clearing operations 

 probably did not markedly reduce the amount of mast available for water- 

 fowl because nut-bearing trees such as oaks, grow further from the 

 water's edge than softwood, according to Dr. Frank C. Bellrose, Water- 

 fowl Biologist, Illinois Natural History Survey, Havana, Illinois. 

 Starrett (1971) indicated that the reduction of diversion from Lake 

 Michigan after 1938 coupled with the higher dams on the river have re- 

 sulted in a decrease of average current velocity from about 1.25- 

 2.50 miles per hour prior to 1908 to 0.6 miles per hour in 1966. 



Richardson (1921a) indicated that abundant populations of finger- 

 nail clams in the Illinois River were generally found in areas of 



4" 



