Depth and Breadth yi 



That of the University of Indiana is on Winona Lake, 

 a shallow hard water lake of irregular outline, having 

 an area of something less than a square mile, an eleva- 

 tion of 8 ID feet, a maximum depth of 8i feet and a 

 transparency (Secchi's disc) varying with the season 

 between 7 and 15 feet. Preliminary survey work has 

 been done on many of the other lakes of Indiana. 



That of the University of Iowa is on Okoboji Lake. 



That of the University of Montana is on Flathead 

 Lake, a cold mountain lake some thirty miles long by 

 ten miles broad having an elevation of 2916 ft. and a 

 maximum depth of 280 ft. 



Under the direction of the Biological Board of Can- 

 ada, which has its headquarters at the University of 

 Toronto, much survey work is being done on Canadian 

 lakes throughout the interior provinces, in cooperation 

 with that University, with the provincial universities 

 of Manitoba and Saskatchewan, and with Queen's Uni- 

 versity at Kingston. This work, like the survey work 

 of the U. S. Bureau of Fisheries, is mainly done from 

 temporary field stations, without the establishment of 

 permanent laboratories. 



Depth and Breadth — The depth of lakes is of more 

 biological significance than the form of their basins; 

 for, as v/e have seen in the preceding chapter, with 

 increase of depth goes increased pressure, diminished 

 light, and thermal stratification of the water. Living 

 conditions are therefore very different in shallow water 

 from what they are in the bottom of a deep lake, where 

 there is no light, and where the temperature remains 

 constant throughout the year. Absence of light pre- 

 vents the growth of chlorophyl-bearing organisms and 

 renders such waters relatively barren. The lighted top 

 layer of the water (zone of photosynthesis) is the pro- 

 ductive area. The other is a reservoir, tending to 

 stabilize conditions. Lakes may therefore be roughly 



