. . . the mussel fauna of the Alton pool was affected 

 adversely by pollution between 1912 and 1930 but . . . con- 

 ditions for mussels probably have worsened since 1930 . . . 

 (1971: 356) 



Mussel populations in the lower Illinois River were being adversely 

 affected prior to the completion of the navigation system. From 1912 

 to 1930 the number of species recorded from collections in the river 

 near Meredosia fell from 31 to 19 (Table 6 ) . 



One early detrimental influence was the increased flow of sewage 

 and industrial effluent from Chicago and Peoria as mentioned in the 

 Water Quality Section. Although Alton Pool is the farthest removed 

 from this influence, Starrett felt that upstream domestic and in- 

 dustrial pollution were the prime limiting factors for the mussels of 

 this pool (1971: 356). 



Overharvesting in the initial years of the pearl-culture industry 

 also played a role. Danglade reported that as early as 1912 mussel 

 fishermen near Meredosia complained that the "river is playing out," 

 and in 1914 the area from Peoria south to Kampsville was depleted in out- 

 put of mussels (1914: 17, 21). 



Danglade (1914: 47) also felt that land reclamation was affecting 

 the mussel resource: 



The levees which have been heretofore and are now being 

 constructed, particularly in the lower stretches of the river, 

 reduce to a large extent the breeding grounds of the valuable 

 species of fishes and incidentally affect the future supply 

 of the mussels /reduction of fish hosts/. 



Between 1899 and 1914 in Illinois the bottomland areas protected by 

 levees increased from 6,700 acres to 124,205 acres (Forbes and Richard- 

 son, 1919: 146). This trend continued and from 1920 to 1931 the levee 

 acreage increased from 771,312 acres to 994,327 acres (Stewart, 1931: 37). 



The current velocity of the Illinois River has been reduced, and 

 Starrett attributes this reduction to the navigation dams and reduced 

 diversion of Lake Michigan water from previous levels (Starrett, 1971: 272), 



41 



