no areas other than those mentioned where unfavorable chemical con- 

 ditions were found, although \cLthout doubt they exist in Detroit River 

 near sewer outfalls. Such areas probably constitute a small part of 

 the total area available to the fishes in the river. 



It is difficult to evaluate conditions with respect to 

 oxygen and carbon dioxide in terms of their effect on the fishery of 

 the lake, but it is doubtful whether fishes have been killed in 

 large numbers by such conditions. As mentioned previously, they are 

 able to migrate from waters low in oxygen, and thus escape the more 

 serious effects. The undesirable effect, then, seems to have been 

 the reduction of the area available to those species which require an 

 abundant supply of oxygen. If space were a limiting factor, this 

 reduction could be considered as positively harmful to the fishery. 

 However, in view of the small area adversely affected, it is 

 questionable whether space has limited the number of fish which the 

 lake can maintain. If this question be answered in the negative, 

 then the only obvious harmful effect would be the additional expense 

 and inconvenience to fishermen in setting nets farther from their 

 base of operations in the polluted areas. As an offset to this, 

 may be mentioned the possibility that conditions in the polluted 

 areas have resulted in an increase of the more tolerant, although less 

 desirable, species. On the whole it seems improbable that low oxygen 

 and the associated chemical characteristics has been an important 

 factor in depletion of the fishery. 



It will be necessary to consider another factor, namely, the 

 presence of poisonous chemicals derived from industrial wastes. 

 Evaluation of this factor is even more difficult because of our nearly 

 total lack of knowledge of the kind and abundance of poisons present. 

 Conclusions must be made with caution because it is well known that 

 certain chemicals may be harmful to fishes in extremely dilute solution. 



In all probability, strong alkalies and acids were not 

 present in high concentration, for determinations of acidity or alkalinity 

 to phenolphthalein, and of pH, were never extremely high or extremely 

 low. The work of Donaldson and Furman (1927) shcvjs that phenol was 

 present in less than one -half of the samples taken near Toledo Harbor 

 Light and near the mouth of Detroit River. The maximum amount found 

 was $2 parts per billion. Shelford (1917, p. 395) reported that a 

 concentration of 70-75 parts per million was required to kill a small 

 sunfish in one hour. Donaldson and Furman found that the strongest 



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