178 
The wind conditions on the river and the lakes adjacent to 
it—which are generally.elongated in the direction of the main 
stream (PI, II.)—are somewhat peculiar. Owing, it may be, to 
the configuration of the river valley, or perhaps still more to 
the bordering forest of the contiguous bottom-lands, the pre- 
vailing direction of the wind is either up or down the river or 
lake, especially during the summer season. The effect of an 
up-stream wind is greatly to increase the disturbance of the 
surface when wind and current are thus opposed. These winds,. 
when prolonged and violent, decidedly affect the levels of the 
different parts of the lakes, and, for example, in Thompson’s 
Lake (PI. II.) determine at low-water levels whether the lake 
shall discharge its waters.into the river or itself receive an 
access of river. water. Owing to the mobile condition of the 
abundant bottom deposits, at low stages the winds also add 
very much to the silt in suspension in the water, and thus hin- 
der the penetration of light. 
The effect of varying sky conditions lies primarily in their re- 
lation to the temperature of the water, but is due in a less degree 
to the influence of light upon the multiplication of chlorophyll- 
bearing organisms—the primal food supply of the plankton— 
and upon the movements of these and other plankton organisms. 
The abundant silt in suspension in waters of the river and most 
of the adjacent lakes doubtless hinders the penetration of the 
sunlight, but modifies to a much slighter extent its effect upon 
temperatures. Wind and sky conditions combine to favor or 
prevent the appearance of the ““water-bloom.” This is a char- 
acteristic green scum which coats the surface of the river, and 
occasionally of the lakes, on still, warm days in midsummer. 
On cloudy or windy days the minute organisms (Huglena, Chlam- 
ydomonus, etc.) which form the bloom do not rise to the sur- 
face. The conditions of wind and sky are thus important fac- 
tors in the economy of limnetic life and, by reason of their rel- 
atively greater effectiveness in the river and its adjacent 
waters as contrasted with the typical lake, add to the elements 
of instability in the fluviatile environment. 
