22 New York State 



Example of Illinois River 



The effects of stream pollution on the aquatic fauna are well 

 illustrated by the record of Forbes and Richardson (1913) of work 

 done on the Illinois river. A simple group such as the mollusks, or 

 particularly the river mussels, which have a restricted range of 

 movement, furnishes the following characteristic data taken from 

 the extended records of the river study. At Morris, 9 miles below 

 the junction of the uncontaminatecl Kankakee and the Des Plaines, 

 heavily polluted by the waters of the drainage canal which enter 

 this stream 20 miles above the junction, the record states, " The 

 search for mollusks yielded seven species of mussels, all the speci- 

 mens dead, however, except for one collection made in Mazon 

 slough." At the Marseilles dam, 17 miles below Morris " no living 

 Unios were secured either above or below the dam, although the 

 mussel-bar was diligently used in both places/' At Ottawa " diligent 

 use of the crowfoot dredge in various situations brought to light no 

 living mussels except a bar in Fox river water just outside the 

 mouth of that stream. Here two species were obtained alive, and 

 dead shells of eight other species, * * * indicative of an environ- 

 ment still difficult for mollusks." At La Salle " thirty-six specimens, 

 representing ten species (of mussels) included twelve living speci- 

 mens of S species only. * * * The large proportion of dead 

 specimens, as compared with ratios obtained farther down the stream, 

 indicate unfavorable conditions for mussels." At Spring Valley 

 " shells of s species of mussels were dredged from the bottom — all 

 dead, however, except one specimen." At Hennepin "seventeen 

 species of mussels were collected alive and five others were repre- 

 sented only by dead shells. * * * The number of living shells as 

 compared with dead ones is in marked contrast to the conditions 

 found above." " This was the first station at which the life of the 

 river may be said to have found virtually normal conditions " in 191 2. 



As the last point is more than 60 miles from the first record given, 

 one can see how slowly the stream assumes normal conditions in the 

 face of the addition of such a mass of sewage as is introduced by 

 the Chicago drainage canal. If the data for more active species had 

 been used, they would have shown that such forms are lacking, 

 having been driven away by the adverse conditions, or having suc- 

 cumbed to them. In most such cases, since the animals have not 

 hard shells like those of the mussels to leave behind as silent 

 witnesses of the unsuccessful struggle against an unfavorable 

 environment, their absence would be the only evidence obtained by 

 field observations of the unfitness of the region for life of that sort. 



