610 U. S, BUREAU OF TISHERIES 



bering, sawdust, bark, and logs were thrown into the water, and often 

 streams were blocked with this refuse. The bottoms of the lakes are 

 still strewn with this debris, and in stormy weather the nets in shallow 

 water are in danger of destruction from the logs and bark, which 

 have been preserved in the cold water for the last five decades and 

 are washed hither and thither by the waves. These substances 

 have probably long since ceased to be chemically active, but their 

 mechanical effect in smothering the bottom can not be negligible. 



In later years the pollution of rivers and bays by modern industrial 

 plants has made barren some of the most productive fishing grounds, 

 and the continuation of the evil is not only preventing the recovery 

 of these grounds but is spreading its effects. The dumping of ashes 

 into the lakes by steamboats must also have an effect, even on waters 

 so extensive in area as those of the Great Lakes, especially when 

 one considers that the tonnage of shipping that annually passes 

 through the Soo locks alone is greater than that through the Panama 

 Canal. The total weight of such waste must every year run into 

 thousands of tons, and so generally is it distributed that it is not 

 uncommon to pick up clinkers in the gill nets in deep water. 



The practice of dumping fish offal into the lake, even where gulls are 

 at hand to feed on it, is also to be deplored. The guUs are not always 

 hungry enough to consume even such particles as float and those that 

 sink lie on the bottom for months, decomposing but slowly because 

 the water is of such low temperature. There are laws prohibiting 

 the dumping of fish refuse, but it is not surprising that such laws are 

 not strictly adhered to when their violators are constantly and in 

 every way reminded of pollution from more noxious sources. 



The effects of this pollution are mechanical or chemical, or both. 

 No one can defend the introduction into the lakes of substances that 

 smother the bottom, but it is possible to argue in favor of certain 

 forms of chemical pollution. The argument must be drawn from 

 analogy of the effects of such chemicals in small lakes, but since the 

 conditions in shallow lakes are so radically different from those in 

 bodies of water like the Great Lakes that they even maintain an 

 entirely different fauna it must be admitted that a strict analogy 

 is not possible. The fact that pure water will not maintain aquatic 

 life is generally known, and it is a conspicuous feature of the waters 

 of the Great Lakes that they are relatively so very pure. The 

 (juality of the water, within certain limits, of course, affects fish only 

 indirectly by influencing their food. In the case of the Great Lakes 

 we know that prior to human interference in their economy the 

 animals that comprised the food of the typical Great Lakes' species 

 were sufficiently aoundant to support a fish population vastly denser 

 than that of to-day, and it must follow that to introduce into the 

 water foreign substances of unknown effect may be deleterious to 

 this food supply. 



WASTEFUL FISHING METHODS 



Even though the fishermen may be justified in their complaints 

 against others for spoiling the waters for fish, they have no one but 

 themselves to blame for the wasteful fishing methods that have 

 been one of the main factors in the decline of the fisheries. It has 

 often been recorded how sturgeon, herring, and other fish, and im- 

 mature whitefish and trout were originally destroyed because they 



