IMPROVEMENT OF LAKES AND STREAMS . 41 



of less competition. Owing to the tendency of many species to move 

 upstream or downstream, even to great distances, continued stocking 

 is necessary in some heavily fished waters. There is much less danger of 

 overstocking in streams than in lakes. 



The improvement of lakes and streams for the purpose of better 

 fishing is one of the fundamental phases of fish management and con- 

 sists of improving spawning conditions, carrying capacity, and the 

 conditions for meeting the specific needs of the fishes for which the 

 waters are managed. The existing conditions in the waters for fish life 

 must first be measured in order to determine those needing improve- 

 ment. In all cases the cost of improvement must be considered in order 

 to determine whether the results will justify the expenditures. In many 

 northern waters the expense would be so great that it would be im- 

 practicable to attempt to remedy certain unfavorable conditions known 

 to exist. 



