OUTLINE OF STUDY. 5 



These collections were continued through a period of two years 

 and a half. 



Collections at a similar interval of two weeks were also made 

 on Green lake. Green lake was selected for comparative work, 

 partly because of its convenient location, but mainly because its 

 conditions are so different from those of Lake Winnebago>. 



Green lake is situated in Green Lake county, about 25 miles 

 west of the southern end of Lake Winnebago. It is about 7% 

 miles long, with a maximum width of 2 miles. Nearly the 

 whole lake is over a hundred feet in depth, and the western part 

 has a maximum depth of 237 feet. The shore slopes are, for 

 the most part, very abrupt, only a small part of the shore being 

 swampy. The waters of Green lake are exceedingly clear, 

 rarely being markedly discolored by vegetable growths, while in 

 Lake Winnebago during most of the year the water is much dis- 

 colored. On account of the small depth, of Lake Winnebago, 

 storms disturb its water to the very bottom over most of its area, 

 while in the depths of Green lake there is a large body of water 

 which is never appreciably affected even by the severest storms. 

 Because of its depth Green lake has a distinct u thermocline" 

 during the summer months, and the water at the bottom has an 

 annual range of temperature of only about ten degrees Fahren- 

 heit. Lake Winnebago, on the other hand, has, during the sum- 

 mer, a, nearly uniform temperature from top to bottom. 



Lake Winnebago, because of its slight depth, and the fact 

 that the whole body of water is so easily affected by storms, 

 becomes wanned much earlier in the spring than does Green 

 lake, and cools off with corresponding rapidity in the fall. The 

 result is that Lake Winnebago is covered with a thick coat of 

 ice long before Green lake is frozen over. 



Green lake is seldom covered with ice before the first of 

 January, and parts of the lake sometimes remain open through 

 the whole winter. As a result of the late freezing, the ice never 

 reaches the thickness on Green lake that it does on Lake Win- 

 nebago. Because of its great depth, and the consequent exist- 

 ence of a thermocline in Green lake in summer, this body of 

 water has a true "abyssal" fauna, organisms which can exist 



