74 TROUT FISHING 



the north shore yielded many trout ; but 

 now a rise is rare. 



In order to understand the phenomena 

 of sport in lakes, it is desirable that we 

 should first realise that still water differs 

 from running water in an important 

 respect. A stream is of the same tem- 

 perature all through. It is just as cold, 

 or as warm, on the surface as at the 

 bottom ; just as cold, or as warm, at the 

 sides as in the middle. A lake lacks this 

 equality of temperature. Its waters are 

 much less quickly transfused. It is 

 obvious, for example, that if in April 

 there is a sudden freshet from the high 

 lands where snow still lies in drifts and 

 corries, all round the points at which the 

 hill streams enter there will be places where 

 the lake is colder than it is in the middle. 

 There is a still more powerful though 

 less observable cause for inequality of 

 temperatures throughout a lake. We 

 have seen that before ice begins to form 

 on still water the body of the water has to 

 be reduced to freezing-point. Waters 



