The following species were most abundant in one or both of the two 

 middle pools of the river, La Grange and Peoria Pools, which have the 

 most connecting lake area: gizzard shad, carp, river carpsucker, small- 

 mouth buffalo, bigmouth buffalo, black buffalo, yellow bullhead, green 

 sunfish, bluegill, largemouth bass, white crappie, black crappie, and 

 freshwater drum. 



Gizzard shad and carp were generally abundant throughout the river. 



Black bullheads were abundant at one station, Ballard Island Chute, 

 Marseilles Pool (mile 247.8-248.2), which apparently provides preferred 

 habitat for this species. 



Gamefish populations declined during the low water years 1962-1964, 

 and recovered following the high water years 1971-1973. Largemouth bass 

 populations in La Grange and Peoria pools did not recover to 1959-1962 

 levels. The recovery appears attributable to improved oxygen levels in 

 the river, and perhaps to increased dilution of toxic materials, and 

 demonstrates how rapidly fish populations respond to improved conditions 

 in the river. 



The commercial and sport fisheries in the Illinois River have 

 generally declined from levels around the turn of the century. The 

 decline is attributable to a loss of habitat and increasing pollution. 

 Habitat was lost due to leveeing and draining of bottomland areas in the 

 period 1903-1926 and due to sedimentation in the remaining areas. Sedi- 

 mentation has resulted in undesirable habitat modification, as well as 

 habitat reduction. 



Northern pike, yellow perch, and walleye ( Stizostedion vitreum 

 vitreum) were once abundant in the river but are now rare or limited in 

 their distribution. Yellow perch populations have declined probably as 

 the result of the disappearance of beds of aquatic plants and disap- 

 pearance of clean sand or pebble substrates perch use for spawning. 



In the past, the bottomland lakes and backwater areas offered 

 havens for fish and fish food organisms, as the river became increasingly 

 polluted. Now dissolved oxygen levels in the upper river seem to have 

 improved somewhat, while the lakes have filled with sediment that 



75 



