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, 

 an elevation of 810 feet, a maximum depth of 81 feet 

 and a transparency (Secchi's disc) varying with the 

 season between 7 and 15 feet. 



That of the University of Iowa is on Okoboji Lake. 

 That of the University of North Dakota is on Devils 

 Lake, an alkaline upland lake (salinity 1%) having an 

 area of 62^ square miles and a maximum depth of 25 

 feet. The salt-marsh ditch-grass {Ruppia maritinia) 

 is the only seed plant growing in its waters. 



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. 



That of the University of Utah is on Silver Lake 

 (altitude 8728 ft.) some twenty miles from the Great 

 Salt Lake. Six small nearby mountain lakes all have 

 an altitude of more than 9000 feet. 



Doubtless, with the growing interest in limnological 

 work, other lakeside stations will be added to this list. 

 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 



