274 ILLINOIS ACADEMY OF SCIENCE 



immense sewer bringing dowoi the Chicago sewage. Both 

 rivers, but especially the DesPlaines, are full of the char- 

 acteristic algae and other vegetation which grow in such 

 waters, and the combination of a copious vegetation with 

 the sewage has effectually killed off all the mussels in 

 the vicinity. Not a single living specimen could be found 

 in either river; but there were hundreds of dead shells 

 along the banks, most of these old and bleached, but still 

 capable of identification". This statement, of course, 

 applies only to the lower part of the Kankakee River 

 where the influence of the polluted DesPlaines has 

 worked upstream for some distance. The Kankakee for 

 the most part is a highly productive stream with a high 

 rate of dissolved oxygen, in fact, the water is super- 

 saturated with this life-giving element. 



In the Maumee River (Wilson and Clark, 1912, pp. 

 26, 28) shell beds were found which had probably been 

 killed by the refuse from gas works near the junction of 

 the St. Marys and St. Joseph rivers. ' ' Spots of tar were 

 found on dead mussels some distance below this point. 

 The water was covered with an oily scum in places and 

 a tarry odor was perceptible for several miles down the 

 river". Lower in the river the mussels were showing the 

 ■effect of increased pollution of the stream by sewage. 



Pollution is worst and usually most deadly to animal 

 life during periods of low water and in winter when the 

 amount of water in the stream is small and the decom- 

 posing organic material has less water to deprive of its 

 dissolved oxygen. During times of floods the putrescent 

 material is also carried down stream for many miles and 

 cotaminates areas not previously affected. 



While all clean-water forms of animal life are more or 

 less affected by sewage pollution, the decomposition of 

 the organic matter abstracting dissolved oxygen from the 

 water and rendering it unsuitable for aquatic life, the 

 fish, river mussels, and crayfish are particularly affected, 

 most fish being especiall}^ sensitive to contaminated 

 water. Some fish (as the brook silversides, LahidestJies 

 sicculus) are notably sensitive, while others (as the 

 black bullhead, Ameiurus melas) will endure water that 



