1825. The Wei land Canal, which was opened in 1829, connected Lake Ontario 

 to the upper lakes. Previously the passage of fish between Lakes Ontario 

 and Erie was blocked by Niagara Falls. Although no biological changes were 

 noticed for many years after the opening of the canals, the stage was set 

 for dramatic and catastrophic changes to occur decades later (Aron and 

 Smith, 1971). 



The chemical characteristics of the open waters of the lakes were 

 assumed to be essentially the same at the end of the 19th century as at the 

 beginning (Beeton and Edmondson, 1972). Although the settlement of the 

 Great Lakes basin had advanced rapidly in the 19th century, from a popula- 

 tion of a few thousand early in the century to over 10 million in 1900 

 (Table 3), the effects on water quality in the lakes were yet to be felt. 



By 1900 man, in less than 100 years, had placed the following stresses 

 on the biological communities of the Great Lakes: siltation of streams; 

 blockage of tributaries; increase in stream temperatures; and establishment 

 of exotic species. In addition, he had removed barriers to migration 

 between the lakes; had established fisheries capable of overexploitation of 

 most species in all the lakes; and had begun using the lakes as the 

 receiver of man's domestic and industrial waste. 



TABLE 3. ESTIMATED POPULATION (MILLIONS) IN GREAT LAKES 

 BASIN - 1900- I960 9 



Lake basin 1900 1925 1950 1960 



Superior 0.4 (50) b 0.6 (33) 0.8 (12) 0.9 



Michigan 4.0 (-20) 3.2 (50) 4.8 (23) 5.9 



Huron 1.0 (20) 1.2 (25) 1.5 (33) 2.0 



Erie 3.0 (93) 5.8 (48) 8.6 (17) 10.1 



Ontario 2.0 (25) 2.5 (20) 3.0 (33) 4.0 



Total 10.4 (28) 13.3 (41) 18.7 (22) 22.9 



a From Beeton, 1969. 



b Numbers in parentheses indicate percentage change in 

 the ensuing time interval. 



203 



