A STUDY OF TWIX LAKES, COLORADO. 



159 



temperature of the water in some of the other affluents was as follows: Willis Creek, 

 12.6= C. (oi.l- F.); creek flowing into Elbert Bay, 25. .5^ C. (78° F.); creek on Koyston 

 Point, 12.0^ C. (54.5- F.), and the water of a spring on Royston Point had a tempera- 

 ture of 6.4- C. (43.5- F.). Lower Lake is a little more than three times as large as 

 Upper, and the wind is thus much more efl'ective in disturbing the water of the super- 

 thermocline region. As one result this stratum of water was al)out two and a half 

 times as thick in Lower Lake as in Upper. On August 7, 1903, for example, it was 

 3 meters (10 feet) thick in Upper and 8 meters (26 feet) thick in Lower Lake. 



Likewise this greater disturbance of the water would affect the subthennocline 

 by producing currents strong enough to affect the water throughout its entire depth. 

 So large a portion of l.iower Lake is comparatively shallow that its average depth is 

 much less than that of Upper Lake. Thus, the sun is much more effective in warm- 

 ing the water of the former. In the shallower water the light that is not absorbed 

 b}' the water itself is changed to heat when it reaches the bottom, and most of this 

 heat will be absorbed l)y the water above, so that nearly all the sun's energy is used 

 up in warming a tolerably thin stratum. Where the water is deeper the light will 

 penetrate to a greater depth and the same amount of energy falling on an equal area 

 will he distributed through a much larger quantity of water and will thus not raise 

 its temperature so much. 

 The following table shows two sets of temperature observations on each lake: 



Temperatures in Twin Lakes in summers of 190^ and 1903. 



AQUATIC VEGETATION. 



Potamogeton was found to be more abundant than any of the other large forms 

 of aquatic plants. It grew in considerable abundance at the west end of L^pper Lake, 

 along the north side of Lower Lake, from North Bay west, and also in the shallow 

 water of the east end. In some places where the water was 10 feet (3 meters) deep 

 it came almost to the surface. Three different species and one variety wei'e found, 

 Potamogeton niittallii^ P. perfoUatus, P. ptrfoliatic^ ric/iardsonu, and P. pra^Iongus. 

 One or two species of Carex were found in the pools of the swampjr meadow west of 

 Upper Lake and in a very few places along the edges of the lakes. Batrachium 

 trichophyllum also was found in the pools and in a few places in the lakes. 



