the area within the outer limit of the 7,one o? lif;ht pollution had a 

 bottom free from or,.anic debris. The conclusions refiardint, the extent 

 of the two zones of pollution are shown in Figure 28j their areas 

 are as follows: moderate pollution, 31.3 square kilometers (12.1 

 square miles) j light pollution, 122,0 square kilometers (Ii7.1 square 

 miles). The total area is 153.3 square kilometers {~>9.2 square miles). 



Areas of the zones of pollution 



Table 100 shows the areas included in the zone;; of heavy, moderate, 

 and light pollution at the mouths of Maumee, Raisin, and Detroit Rivers. 

 These areas were obtained by the use of a polar planimeter on the large- 

 scale map from which Figure 23 was reproduced. Only at the mouths of 

 Matunee and Raisin Rivers was there heavy pollution as defined in this 

 report, and at River Raisin the area of the zone was very small. Thf 

 area of moderately polluted bottom also v;as small at the mouth of this 

 river, but at the other two rivers considerable areas were included, 

 making a total of Ii6,3 square kilometers (17.9 square miles), as compared 

 to a total of 2$, 2 square kilometers (9.7 square miles) for the zones of 

 heavy pollution. The zones of light pollution were the largest in each 

 section; the combined area was 191. h square kilometers (73.9 square miles). 

 The areas of the three zones combined for each section were as follows: 

 Maumee Bay Section, 76,9 square kil«^meters (29.7 square miles); River 

 Raisin Section, 32,7 square kilometers (12,6 square miles); Detroit River 

 Section, 153.3 square kilometers (59.2 square miles); giving a grand total 

 of 262.9 square kilometers (101.5 square miles), or 7.7 per cent of the 

 watfr area of VJestern Lake Erie exclusive of Sandusky Bay. Of the arei. 

 •dthin the zones of pollution, 72.8 per cent fell within the zone of 

 light pollution, and an unknotm but considerable part of this zone was 

 free of organic debris . 



Effects of pollution on the fishery 

 General Statement 



The extent and degree of pollution in V/estern Lake Erie has been 

 determined with some degree of exactness, but interpretation of the 

 facts in terms of the effects on the fishery must be based largely on 

 conjecture. Sons of the effects of pollution are harmful to fishes 

 and hence to the fishery, while others are clearly advantageous. How- 

 ever, there are no standards by which they can be compared quantitatively 

 to determine the residual effect on the fishery. 



299 



