( Cyanophyta ) declined markedly by a factor of 80 to 100, (f) rotifers 

 declined by a factor of 10, and (g) copepods increased slightly. The 

 decline in blue-green algae may be attributable to increased suspended 

 solids and turbidity in the Illinois River. The diatoms probably per- 

 sisted or increased because they can tolerate the reduced light and 

 increased abrasion associated with suspended sediment. Because the 

 diatoms persisted, and because they are at least as sensitive to toxicants 

 as other algae (such as blue-greens) , the decline in blue-greens probably 

 is not attributable to toxicity. The change in phytoplankton and the 

 increase in the suspended solids load of the lower Illinois River may 

 have impaired the feeding of rotifers, thereby reducing their popula- 

 tions. Rotifers are an important food for the fry of many game fish, 

 such as bluegill, so the reduction in rotifers might have had a 

 significant impact on the growth and survival of fish fry. 



19. Wetland vegetation was inundated when the 9-foot channel project 

 raised water levels and initially created additional water areas. However. 

 new areas were pioneered, resulting in expanded aquatic plant and marsh 

 acreage. 



20. Since increases in water levels can destroy wetland 

 vegetation after it has become established in shallow water and on 

 exposed mud flats in the summer, the stabilizing effects of the dams in 

 most years between 1948-1968 on Pool 26 resulted in excellent plant 

 growth. Pool 25 was subject to frequent and sometimes severe flue-, 

 tuations in 1948-1951, 1954, 1958, 1961, and 1967, which adversely 

 affected wetland vegetation. 



21. The greatest adverse effect of the 9-foot channel project 

 on wetland vegetation has resulted from an increase in turbidity and 

 sedimentation. Plants need sunlight for photosynthesis. Turbidity 



193 



