169] FAUNA OF BIG VERMILION RIVER— BAKER 71 



reduced in number of individuals. An examination made in 1910 failed 

 to discover a single living moUusk 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 a.bout 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 Ontario 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. 



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 



Bylhinia tentaculata Physa Integra 



Galba catascopium Physa oneida 



