1932 ANNUAL REPORT, 1931 49 



must be rigorously controlled. The lake herring travel in schools and are 

 of considerable commercial importance. 



(5) Trout hooks take large quantities of ling. 



6. Pollution 



Systematic studies of suspected sources of pollution, particularly in cities 

 and towns of Ontario, are underway with a view to improving conditions for 

 fish in waters located at such centres wherever improvements are possible and 

 practicable. 



This year pollution studies were carried out at Lindsay, Sarnia. Kitchener, 

 Waterloo, Chatham, Acton, Oakville, Trenton, South River, Coutland and 

 Moore's Cove near Haileybury. The forms of alleged pollution encountered 

 were as follows: Acids, tannery wastes, paper-mill wastes (straw and wood 

 pulp), milk wastes, cyanide, commercial alcohol, creosote, sewage and sugar- 

 beet wastes. 



In the majority of these instances the pollution was found to be either 

 comparatively harmless or the effluents causing the pollution have been eliminated 

 or so treated as to neutralize their harmful effects. Sugar-beet wastes, however, 

 have proved to be especially difficult to control. The same difficulty has been 

 encountered by our neighbours in the State of Michigan. Decomposition of 

 the effluents from these factories requires a great deal of oxygen present in the 

 water of the stream into which the wastes are dumped. In other words, there 

 is a high oxygen demand, and consequently this problem is not easily solved. 

 However, the sugar factories concerned have shown a fine spirit of co-operation 

 and e\ery effort is being made to eliminate these troublesome wastes. 



7. Dams, Screens and Fishways 



During the year an organized survey of dams and other barriers across 

 water-courses to determine the feasibility of introducing fishways was under- 

 taken in the following districts: Algoma, Dufferin, Elgin, Frontenac, Lennox 

 and Addington, Nipissing, Parry Sound, Peel, Simcoe, Timiskaming, Sudbury 

 and \'ictoria. 



The entire question of screening waters which flow through pri\ate lands 

 is at present under consideration with a view to arranging a definite policy of 

 treating such cases. The feasibility of such screens was the subject of study 

 in waters located in Grey and Peterborough counties. 



The law regarding the erection or maintenance of screens or other 

 obstructions across water-courses is defined in Section 41 of the Dominion 

 Fisheries Act. 



8. Water-Levels 



The water-Ie\els of the Rideau canal system at vSmith's Falls were 

 investigated and reported upon, the following areas receiving special attention: 



(a) Reach between Graham lock and Dalton lock; 



(b) Reach between Dalton lock and Killmarnock lock. 



