of navigation dams (Richardson, 1921a). On drying, the bottom muds com- 

 pact, and when the lakes are reflooded, the turbid water generally 

 clears, and the plants can gain roothold in the firm bottom. This ap- 

 proach represents a temporary restoration only. The sediment storage 

 capacity of a lake is limited and the river deposits more sediment during 

 each period of overbank flow. 



Private duck clubs and Federal wildlife refuges along the Illinois 

 River also attempt to reduce water levels in the summer in order to ex- 

 pose mud flats and encourage the growth of moist soil food plants for 

 waterfowl. Once again, a natural drying cycle has had to be replaced or 

 supplemented by pumping, because water levels do not attain the low 

 levels they once did. Such management techniques require energy, equip- 

 ment, and manpower, but are necessary if fish and wildlife populations 

 are to be maintained at existing levels, or if they are to recover to 

 some proportion of the population levels which once existed in the 

 Illinois valley. 



Refuges, unpolluted lakes, and unpolluted tributary streams must 

 be maintained or restored if the river is to be capable of the recovery 

 pattern in the future that it exhibited in 1973-1974, following the 

 high-water period and improved oxygen levels from 1971-1973. When 

 formerly degraded areas are restored, they can be recolonized rapidly 

 by species that are desirable to man, if reservoirs of such species and 

 reservoirs of food organisms for desirable species are available in 

 undegraded pockets here and there in the ecosystem. The refuges main- 

 tained by man have precisely this function. 

 Predict impacts 



Information and methodologies need to be developed to predict the 

 impact of man's future activities on the Illinois River system, so that 

 a rational choice of alternatives can be made. For example, the effects 

 of various future channel improvement schemes and various levels of 

 barge traffic on oxygen levels and turbidity in the main channel and 

 backwaters needs to be predicted. The expected life span and probable 

 future condition of bottomland lakes and marshes should be predicted so 

 that conservation agencies can make a wise selection of new refuge 



