167] FAUNA OF BIG VERMILION RIVER—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, A meiurus melas) 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 Ili- 
nois River has been marked, many species, such as catfishes, red-horse, 
