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trade wastes. Sewage enters the streams from private toilets 

 and cesspools, and in the form of effluents from municipal sys- 

 tems. Owing to its prominence as a public health factor, meth- 

 ods of disposal have been devised by which it will be eventually 

 fully controlled. If unregulated it damages water supplies and 

 manufacturing interests, endangers public health through the 

 contamination of edible shellfish, and is injurious to fish and 

 fish environment. In 1920, after a thorough investigation, 

 the Massachusetts Department of Public Health made a report 

 (House, No. 1115), with recommendations for improving pollu- 

 tion conditions in the Taunton River and its tributaries. 



Trade wastes include all forms of waste material from indus- 

 trial sources. Fish preservation is chiefly concerned with this 

 important type of pollution, which, in addition to rendering 

 water unfit for drinking, bathing and for use in certain indus- 

 tries, directly and indirectly destroys fish life. 



Effect. ■ — Pollution may produce one or more of the following 

 direct effects upon alewives: injury causing death or predis- 

 position to disease, reduction of the oxygen supply in the water, 

 rendering the fish unfit for food and driving them away from 

 the streams. Indirectly it may cause the destruction of eggs 

 and young, reduction of the spawning grounds, changes in bot- 

 tom and vegetation, and limitation of the food supply. 



Adult fish doubtless can stand a much greater amount of pol- 

 lution than is ordinarily believed, and require a considerable 

 quantity of concentrated pollution to kill in large numbers. 

 Even in these cases it is difficult to prove cause and effect, as 

 the damage is largely done by transitory pollution of varying 

 strength and quantity. Little if any pollution occurs in the 

 spawning grounds, and the susceptible young fish can be de- 

 stroyed only as they pass down -stream to the salt water. 



Changes in the physical characteristics of a stream, in food 

 forms, vegetation, oxygen content of the water, and other en- 

 vironmental conditions indirectly affect the fish life. Since 

 slight changes in the water influence the movements of fish, 

 the entrance of chemicals into the streams may have a marked 

 effect upon the migration of the alewife. 



Setcage. — Owing to the scattered nature of sewage pollution 

 in the smaller streams its effect may be disregarded, but in the 



