Stkeam Pollution 15 



a stony or rocky bottom with falls or rapids from point to point to 

 mix it with the air will take on oxygen very rapidly. Once, 

 however, let the current be stopped and the water accumulated in 

 deep, slow flowing masses, the process of purification is almost 

 entirely inhibited so that it proceeds very slowly indeed. This is 

 exactly the condition which has arisen as the streams have been more 

 and more perfectly utilized for water power. The erection of a dam 

 below a series of rapids or ripples, impounding the water to a con- 

 siderable depth and backing it up to a point which in the ultimate 

 development of the stream will represent approximately the base 

 of the dam next higher up, makes of a natural water course with its 

 rapidly flowing current only a series of ponds in which the movemen: 

 Is almost imperceptible. Wastes delivered into the stream when 

 the latter has reached this condition of stability will be precipitated 

 to form a layer on the bottom, the thickness of which is regulated 

 by the amount, and the change in which is reduced nearly to zero. 

 Where in the original condition the stream might have endured the 

 contamination and have been able to effect self purification within 

 a reasonable distance, the new conditions are entirely unfavorable 

 for changes and under them the stream is transformed into what, in 

 these conditions, is simply a series of septic tanks. In these, the life 

 characteristic of pure waters is entirely eliminated and the only 

 organisms which can survive are those of putrefaction. 



Canalization is a necessary feature of our modern industrial 

 development, but pollution, the evil effects of which are seriously 

 augumented by canalization, has no such argument in its favor. 

 Canalization thus provides a new reason for the elimination of 

 stream contamination. 



Influence of Pollution on Aquatic Life 



Let us consider more carefully the effect of stream pollution upon 

 fish life. At another place in the discussion I have taken up the 

 question as to whether the absence of fish from streams is due to 

 pollution or to other causes. In those instances in which pollution 

 is both recognized and admitted, there certainly must have been 

 considerable influence exerted upon the availability of those waters 

 as areas for the existence and propagation of fish. 



If the substances which are discharged into the water are directly 

 poisonous to fish and are poured out in such quantities that even the 

 volume of the stream does not dilute them beyond the point at which 

 the poison is fatal, the entire fish population will be killed or driven 



