receives a large amount of sewage. As early as I898 there was definite 

 chemical and bacterial evidence of pollution at several points in the river, 

 and the subsequent growth in population doubtless has caused an increase in 

 intensity of pollution. The principal source of sewage in the lower part 

 of the river is Toledo, Ohio, situated at the mouth. The population of 

 Toledo in 1930 was 290,718, so that with mean discharge (5,Ul7 second-feet) 

 there would be 5U individuals for each second-foot of river water available 

 for dilution. In periods of low v/ater this figure would be increased con- 

 siderably; during July- Sept ember, 1929, it was 135 per second-foot, and in 

 1930 the corresponding figure was II1U6. The International Joint Commission 

 (1918) concluded that a stream with a discharge of less than h second-feet 

 for each contributing person was unsafe as a source of drinking water unless 

 treated. The wide discrepancy between this figure and those given for Mau- 

 mee River at Toledo during periods of small discharge leads one to expect 

 heavy pollution at the mo<ith, particularly when it is recalled that the 

 water is polluted before reaching Toledo. Inflow of lake water increases 

 dilution in the lower part of the river periodically, so that marked varia- 

 tions in the intensity of pollution in a single day are to be expected. 



The flow of River Raisin has not been measured accurately. From esti- 

 mates of the run-off per square mile made by McNamee (1930, page 56), the 

 mean annual discharge has been calculated to be about 675 second-feet. 

 According to estimates given in an unpublished report by Professor Jacob E. 

 Reighard, the mean discharge for July, August, and September of I9I8, 1919, 

 and .1920, was 197 second-feet. Nothing is known of the discharge during 

 the same period of 1928, 1929, and 1930, when most of the chemical samples 

 were taken in this section. In all probability it was very low in 1930 here, 

 as in Maumee River. There are no large cities contributing sewage to River 

 Raisin, and according to McNamee, (1930) the total sewered population is only 

 37,787. Yet the volume of sewage is large for a stream of such small dis- 

 charge. Monroe, Michigan, with a population of 18,110, is the main source 

 of sewage near the mouth of the river. At times of mean discharge there 

 would be, near the mouth, 27 contributing persons per second-foot; and for 

 the months of July, August, and September (using the mean for I918, 1919, and 

 1920) there would be 92 persons per second-foot. However, these figures do 

 net give an adequate idea of the intensity of the pollution, because as 

 McNamee pointed out, the watershed is characterized by a comparatively high 

 proportion of waste-producing industries for its size. For example, paper 

 mills at Monroe during normal activity discharge volumes of waste which 

 may well approach or exceed the domestic sewage of Monroe in polluting 

 capacity. Periodic inflow of water from the lake should increase dilution 

 in the lower river, but in view of the large amo\int of wastes entering in 

 that region, definite chemical evidence of pollution is to be expected at 

 times of small discharge. 



Detroit River is the principal tributary of Lake Erie. With average 

 'height of water in Lake Huron and Lake Erie, its discharge is approximately 

 20U,000 second-feet. Discharge of the river is not subject to such large 

 fluctuations as the smaller streams. However, according to figures obtained 



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