169] FAUNA OF BIG VERMILION RIVER—BAKER 71 
reduced in number of individuals. An examination made in 1910 failed 
to discover a single living mollusk of any species. Apparently the water 
had reached such a state of concentrated pollution that even the air-breath- 
ing mollusks, which normally come to the surface to take free air, could 
not adapt themselves to this unfavorable environment and were either 
killed or compelled to migrate down the river to a point where pollution 
was less deadly. During the following years, 1910 to 1913, the river was 
visited but no mollusks were found. 
During the summer of 1912, G. C. Whipple, made a study of the effect 
of the sewage pollution on certain animal and vegetal life in the Genesee 
River (Fisher, 1913:179-200). This study was made when pollution was 
at its maximum and during the period when molluscan life had disappeared 
from the lower part of the river. The dissolved oxygen in the lower river, 
below the trunk line sewer, in July and August, when the temperature 
was high and the water low, varied from 5 to 41 per cent of saturation. 
The water at the bottom of the river almost always contained less oxygen 
than that at the surface. On one day in August, the percentage of satu- 
ration in a distance of three miles did not exceed 5 per cent from the 
surface to the bottom of the stream, which has a depth of about twenty- 
six feet. The number of bacteria per cc for this period was 1,650,000 near 
the source of pollution and but 67,000 per cc near the mouth of the river 
where the influence of the pure water from Lake Ontario increased the 
amount of dissolved oxygen. 
In 1917, a large part of the city sewage was diverted to a disposal 
plant situated near the shore of Lake Ontario. Here an average of 32 
million gallons of sewage are treated daily and the treated sewage is dis- 
charged into Lake Ontaric in deep water at some distance from shore. 
It is at once apparent that when this large amount of sewage was discharged 
into the Genesee River in a crude condition, it could not but render the 
water totally unfit for animal life and a menace even to the inhabitants 
who visited the beautiful parks bordering both sides of the lower Genesee 
River. 2 
The result of the diminution in the amount and character of the sewage 
discharged into the river has been that the molluscan fauna, as well as 
other forms of aquatic animal life, have returned and are rapidly taking 
possession of the favorable environments which were in use previous 
to the maximum period of pollution. Collections made in September, 
1919, contained six species, two being water-breathers and four air- 
breathers. 
Musculium transversum Planorbis trivolvis 
Bythinia tentaculata Physa integra 
Galba catascopium Physa oneida 
( 
