167] FAUNA OF BIG VERMIUON RJVER— BAKER 69 



to the lower part of the Kankakee River where the influence of the polluted 

 DesPlaines has worked upstream for some distance. The Kankakee River 

 for the most part is a highly productive stream with a high rate of dissolved 

 oxygen, in fact, the water is supersaturated with this life-giving element. 



In the Maumee River (Wilson and Clark:1912, 26, 28) shell beds were 

 found which had probably been killed by the refuse from gas works near 

 the junction of the St. Mary's and St. Joseph's 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 down the river the mussels were 

 showing the effect of increased pollution of the river by sewage. 



The pollution is worst and usually the 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 decomposing organic material has less water to deprive 

 of its dissolved oxygen. During times of floods the putrescent material 

 is also carried down the stream for many miles and contaminates areas not 

 previously affected. 



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

 by sewage pollution, the decomposition of 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 especially sensitive to contaminated water. Some fish (as the 

 brook silversides, Labidesthes sicculus) are notably sensitive, while others 

 (as the black bullhead, Ameiurus mclas) will endure water that is badly 

 polluted (Shelford, 1918:27; Wells, 1918:562-567). The young fish are 

 relatively more sensitive than the adult fish. It is noteworthy that the more 

 resistant species of fish are inhabitants of sluggish bodies of water, as ponds 

 and shallow lakes, while the least resistant species live in running streams. 

 It seems to be a question of the amount of oxygen necessary for the well 

 being of the fish. 



The ill effect of sewage pollution is most marked on the bottom of 

 bodies of water, where a sludge is formed, often of great thickness (as 

 much as ten feet in some instances), consisting of a mass of soft, black, 

 sediment with a high content of organic matter, in which only a few 

 organisms, normally inhabitants of polluted streams, can live (e.g., septic 

 Protozoa and Rotifera, foul- water algae, and slime worms, Tubificidae). 

 This effect on the bottom is perhaps the most serious phase of stream 

 pollution because the septic condition of this area continues in operation 

 long after the original source of contamination ceases to operate. This 

 sludge formation renders the bottom unfit for clean-water life upon which 

 many fish depend for food. 



The effect of sewage pollution on the fish population of the upper Illi- 

 nois River has been marked, many species, such as catfishes, red-horse, 



