191. ii square kilometers (73.9 square miles). The total area in the three 

 zones of pollution was 262.9 square kilometers (101.5 square miles), or 7.7 

 per cent of the water area of Western Lake Erie exclusive of Sandusky Bay. 

 Of the total area in the three zones of pollution, 72.8 per cent fell within 

 the zone of light pollution, and an unknown but considerable part of this 

 zone was free of organic debris. 



Effects of Pollution on the Fishery 



The extent and degree of pollution in Western Lake Erie has been deter- 

 mined with some degree of exactness, but interpretation of the facts in 

 terms of the effects on the fishery must be based largely on conjecture. 

 Some of the effects of pollution are obviously harmful to fishes and hence 

 to the fishery, while others are clearly advantageous. However, there are 

 no standards by which they can be measured and compared quantitatively to 

 determine the residual effect on the fishery. No attempt will be made here 

 to enter into a detailed discussion of the problem. Briefly stated, the 

 conclusions reached are as follows. Conditions in the lower parts of Maumee 

 and Raisin Elvers, and in small areas of the lake near their mouths, have 

 been made unfavorable or prohibitive to all except the most tolerant fishes 

 by reason of the low content nf oxygen and high content of free carbon 

 dioxide. In addition, considerable areas of the bottom near Maumee, Raisin 

 and Detroit Rivers have been rendered unfit for spawning purposes by the 

 deposition of organic debris, but it should be recognized that a large part 

 cf the polluted area probably never was suitable for spawning because of the 

 deposition of silt. These harmful results of pollution have been offset, 

 partially or wholly, by the increase in plankton organisms which are used as 

 food by all young fishes and the adults of certain species. In view of the 

 tendency of the harmful and helpful effects to balance each other, it seems 

 highly improbable that pollution in the western part of the lake has been 

 the controlling factor in the depletion o f the fishery of Lake Erie. 



