400 American Fisheries Society 



considerable current. Finally, they have not penetrated to the 

 real headwaters of the stream but are all grouped in the lower 

 half of its course. A series of temperature readings taken 

 with some care showed the following situation : 



The east channel of the Copper above the mouth of Clear 

 Creek had on July 22 a temperature of 48.5° F. At the same 

 hour the temperature of Clear Creek fifty yards above its 

 mouth was only 44° F. At the railroad trestle the tempera- 

 ture of the creek had dropped to a level of 42° to 42.5° F. 

 A mile above this and just below the marshy region it was 

 again 44° F. and the same temperature obtained throughout 

 that region. The stream thus showed in the first place that 

 it was 4° cooler than the water of the Copper River at their 

 junction, and that the temperature after falling 2° at the trestle 

 again became warmer some distance farther up at the marshy 

 region. On running a line of temperatures across the stream 

 above the trestle it appeared that near the right bank the water 

 was 43.5° to 44° F. In the center it was full 44° and near 

 the left bank it varied from 41° to 42.5° F. Furthermore, 

 the lowest temperature found was in only one or two limited 

 areas. The exact examination of these places demonstrated 

 the presence of an inflow of seepage water not sufficient in 

 amount to constitute a visible spring or localized at special 

 points, but flowing in over a small area of the bottom in suffi- 

 cient quantity to reduce the temperature very noticeably at 

 that point. 



It should be mentioned in this connection that the tem- 

 peratures are not constant from day to day, for on the follow- 

 ing day, July 23, the stream was about 2° colder, as the tem- 

 perature at the right bank was 42°, in the center 42.5° and at 

 the left bank 39.5° F. On the same day the temperature of 

 the Copper River where the railroad track crossed the east 

 channel was 49° F. 



It was evident that the stretch of Clear Creek above the 

 trestle was supplied along the left bank constantly and largely 

 with seepage water so that the temperature was kept distinctly 



