Forbes & Richardson (1919:140-141) reported an 

 average rise of 2.8 feet at Havana as a result of this 

 diversion, and between Juno and September the level 

 rose an average of ;?.6 feet abo\e piediversion averages. 

 This flooding had several effects on the river. It penna- 

 ncntly inundated tliousands of acres, ultimately kilting 

 bottomland forests. Where trees like the pin oak 

 [Qucnus lialtistiis) and the pecan (Carya illinocnsi\) 

 were in\()l\ed, this meant a loss of food for mallards 

 and wood ducks, but tiiere was also a considerable in- 

 crease in water surface whicli was beneficial to the fish- 

 ery. Forbes and Richaidson (op. cit.:141) conunenlcd 

 that Thompson Lake increased in surface from 1,94;5 lo 

 5,072 acres. As late as 1940, dead snags from this 

 "drowned forest" were still in evidence, hut time and 

 man's later activities have erased most of the traces of 

 the old lakes, sloughs, and bottomland forests which 

 existed prior to the 1900 diversion. 



These same authors (op. cit.:142) give a good ac- 

 count of the effects of this inundation : "This destruc- 

 tion of inshore and alongshore vegetation has been 

 especially conspicuous in the broad belt of deadened 

 trees and shrubs along the banks, especially in the middle 

 course of the stream from Peoria southward. Otiier im- 

 portant effects arc beginning to appear as these dead 

 trees weaken and fall into the water of the stagnant 

 lakes, fouling them, in the hottest weather, with the 

 products of vegetable decay." 



In 1848 the Illinois-Michigan Canal was opened, 

 and in 1907 the Henne]3in Canal connected the Illinois 

 with the Mississipjji. Drainage of bottomlands for agri- 

 cultural purposes followed closely on the heels of the di- 

 version from Lake Michigan. Actually drainage started 

 in a small way prior to 1900 (Mulvihill and Cornish 

 1929:38), but most of the drainage enterprises were ini- 

 tiated between 1903 and 1920. The last levees were 

 started between 1918 and 1921. Initially there were 

 400,000 acres subject to overflow between La Salle and 

 Grafton. At the height of the drainage period iheic 

 were 38 drainage districts and three private drainage 

 areas aggregating 200,000 acres. Spring and Thompson 

 Lakes, long known for their fisheries and their concen- 

 trations of waterfowl, were eliminated as were a host 

 of smaller lakes and sloughs. How drainage and levees 

 have changed the floodplain near Havana is illustrated 

 by Fig. 2. 



There has been some aliandoiunent of drainage 

 districts. Prior to 1920 the Partridge District, across 

 from Chillicothe, failed, and after the Hood of 1926 

 the Chaulauc|ua Levee District near Ha\ana and llie 

 Hig Praiiie Levee District near Heardslown were discon- 

 tinued. These abandonments resulted in a return of 

 8.000 acres to fish and wildlife habitat. 



Another human activity has conspicuously changed 

 the river. Hefore 1900, low dams were buill at Mar- 

 seilles, Henry, Copperas Creek, La Grange, and Kamps- 

 ville. Because they were low, their greatest effect on the 



stream was during periods of low water. During the 

 1930's. higher navigation dams were built at Dresden 

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

 Peoria (11 ft), and La Grange (10 ft). Moreover, a 

 navigation dam on the Mississippi at Alton raised water 

 levels in the Illinois River as far north as Hardin. 



Barge traffic on the ri\er is now very heavy, and 

 there is a conseciuent effect on the turbidity of the water 

 in the main stream and adjacent waters. 



Soil pollution has been present in Illinois River 

 waters since the recession of the last ice sheet. However, 

 the laying bare of the soil in agricultural operations has 

 greatly increased the problem. 



A study of Lake Decatur, on the Sangamon River, 

 a tributary of the Illinois, showed that the rate of sedi- 

 mentation was about 20 percent greater in the decade 

 starting in 1936 than it was in the preceding 14.2 years 

 (Brown, Stall, & DeTurk 1947). In one county above 

 the impoundment row crops increased from 39 percent 

 of the total area in 1924 to 64.5 percent in 1943. There 

 is a probable cause-and-efTect relationship here. This 

 sedimentation is a serious matter to organisms that live 

 in the water as well as to those that use it. Further, it 

 displaces water. Where waters are stilled, the load of 

 silt is dropped, and the water is replaced by .soil. 



In 1964, in the counties drained wholly or in part 

 by the Illinois River 6,220,200 acres were planted to 

 corn for grain which was valued at .$530,288,900. and 

 an additional 3,466,100 acres were planted to .soybeans 

 (Illinois Cooperative Crop Reporting Service 1965). 

 Thus, in these counties 47 percent of the land surface 

 in 1964 was in row crops which leave the soil vulnerable 

 to erosion. 



The streams thai flow into the Illinois have a steeper 

 gradient than dfH-s the Illinois in its central and lower 

 reaches. Since the ri\er is impounded and the gradient 

 is low, it has difficulty carrying its silt load. Therefore 

 a tremendous amount of this turbid burden is deposited 

 in the remaining floodplain lakes when spring flood- 

 waters top the low natural banks. An example of the 

 seriousness of siltation is evident in the study made In- 

 stall & Melsted (1951) of Lake Chautaucjua, They 

 found that in a 23.8-year period the sediment had 

 reduced the storage capacity of this artificial lateral 

 bottomland lake by 18.3 jjercent. nearly one fifth. Other 

 bottomland lakes are steadily diminishing in size and 

 depth as sediments continue to be deposited in spite of 

 soil conservation measures. 



The basic reason for the 1900 diveision of Lake 

 Micliigan water into the Illinois waterway was to dilute 

 sewage and transjjort it away from Chicago. Since that 

 time the treatment of sewage in the Chicago area has 

 been greatly impro\ed, but the rich effluent still affects 

 the waters of the waterway b(4ow the city (Keup. In- 

 gram, Geckler, & Homing 1965). Moreover, the other 

 cities within the Illinois River basin have grown, and 

 make their increasing demands on and contributions to 

 the stream. 



