Depth and Breadth 71 



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. 



That of the University of Iowa is on Okoboji Lake 

 near Milford, Iowa. That of the University of Minne- 

 sota is on Lake Itasca, the source of the Mississippi 

 River, in Itasca Park. That of the University of Vir- 

 ginia is at Mountain Lake (altitude 4000 ft.). That of 

 Brigham Young University is on Utah Lake near Provo, 

 Utah. That of the Tennessee Academy of Science is 

 on Reelfoot Lake (a large shallow lake formed by an 

 earthquake in 1811) near Memphis. 



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 we 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 



