1288 



BULLETIN OF THE BUREAU OF FISHERIES. 



lake contains a great amount of fermentable material, and the oxygen disappears 

 from the bottom water early in the spring. The lake is so small that the ther- 

 mocline lies very close to the surface, remaining at 4 meters or above until late 

 in the sumrper. Were it not for the manufactured oxygen, the entire body 

 of water below the thermocline would be uninhabitable. The maintenance of 

 the stock of this gas by the presence of the algse doubles the thickness of the 

 habitable stratum during the summer and the early part of the autumn. Figure 

 1 7 also shows the effect of the manufacture of oxygen on the dissolved carbon- 

 ates; but that matter is too complex to be discussed here. 



Ch 

 C T 46 48 so 52 54 



p 6 4 2 2 4. ^ 8 10 lg 14 16 I8.g0 2gg4 



I 



2 

 3 

 4 

 5 

 6 

 7 



a 

 9 

 10 

 II 



12 

 13 

 14 

 15 

 16 

 17 

 18 

 19 

 20 

 21 

 22 



Fig. 14. — North Lake, east part, July 30, 1906. 



I have spoken of Thousand Island Lake as a characteristic " lake-trout lake." 

 So far as our observations go, the lake trout in northeastern Wisconsin is found 

 only in lakes of this type; yet observations made in the summer of 1908 in north- 

 western Wisconsin show that the fish can exist in lakes of a type which would 

 seem to be unfavorable to it. I give a diagram of the conditions in Hammill's 

 Lake (fig. 20), a small body of water in northwestern Wisconsin, which contains 

 a few lake trout that have been introduced. Their presence in the lake shows 

 that they can exist in a body of water in which the oxygen extends some distance 



