9 
waters from the Hudson Bay drainage was instituted. A diversion of 1,400 c.f.s. 
by way of Long Lac into Lake Superior and another of 3,600 c.f.s. from Lake 
Nipigon into Lake Superior inaugurated in 1943 total to an inflow of 5,000 c.f.s. 
Langlois (1952) states that this diversion may have raised the level of Lake 
Erie by 3 inches. 
Other waters have been tapped into the Great Lakes system through canal 
development. The Chicago Drainage Canal, Wabash-Erie Canal, Miami-Erie 
Canal, Ohio-Erie Canal, Erie Barge Canal, Welland Canal, and Trent Canal, all 
attach themselves to the Lakes. Even though they may have had no effect on 
levels, each has in it the possibility of changing the physical environment of the 
waters. 
Then there are normal fluctuations in the Lakes. Tides occur, but they 
are of minor consequence; in Lake Michigan they apparently amount to a dif- 
ference in levels of about 5 centimeters. More important than tides are fluc- 
tuations in levels resulting, it is thought, from such things as barometric pres- 
sures and winds. Langlois (1952) states that the extreme condition on Lake 
Erie occurred when the waters rose 7 feet at one end and lowered an equal a- 
mount at the other, making a total differential of 14 feet. These fluctuations 
are of considerable importance. They may affect the biological complexes in 
the Lakes directly or they may, through increased shore line erosion, affect 
them indirectly. Other changes in level, such as that represented by the high 
water of 1952, are apparently due to runoff from the watershed into the Lakes. 
There are many other factors which have a bearing on the physical en- 
vironment. Almost anything which changes the primitive picture in the water- 
shed does this. The erection of dams, the building of weirs, the construction 
of levees, changes in the drainage pattern, all of these and other changes may, 
through chain reaction, affect the Great Lakes. 
CHANGES IN THE FISH POPULATION 
Now let us turn to the fish populations themselves. Are they the same 
as they were originally? If not, have any important changes taken place? 
Not only have the physical factors undergone a shift, but the kinds and 
numbers of fishes have also. Several species are no longer important to the 
fishery. The blackfin chub, lake sturgeon, and lake trout in Lakes Huron and 
Michigan, and the Atlantic salmon in Lake Ontario have disappeared or have 
been greatly reduced in numbers. 
On the other hand, other species have invaded in one way or another. 
The alewife, the smelt, the eel, the carp, the goldfish, the rainbow trout, the 
brown trout, the sea lamprey (which is not a true fish), and other smaller spe- 
cies have appeared in the waters. Some were purposefully placed there; others 
appeared accidentally or incidentally. 
The alewife is a marine species which differs from its seagoing relatives 
