heavy irrigation use and this water used solely for fish production; 

 that is, if this water could be allowed to pass down a stream course 

 without being diverted for other uses. 



Lake Habitat 



A lake and a stream are entirely different types of aquatic 

 habitat; nevertheless, there are a great many similarities between 

 requirements of fish in these habitats, and many of the arguments 

 given in the previous section on streams are equally applicable to 

 lakes. 



In lakes, as in streams, fish require clear, pure water with suit- 

 able chemical balance. The lakes of the state are even less con- 

 taminated today with pollutants than are the streams, but the 

 potential for such contamination is high as economic developments 

 progress. As population pressures in Montana increase in coming 

 years, anglers will become more and more dependent upon the State's 

 lakes for their recreational fishing. Here again, Montana is in need 

 now of legislation that will provide adequate protection against 

 pollution so that contamination of the lakes of the State may be 

 prevented. This will be far more fair and desirable than passing 

 foul waters on to the next generation, thus forcing them to take 

 corrective measures for their forebearers' negligence. 



The stream fish populations of Montana are not any more 

 subject to decimation from construction of impoundments than are 

 lake fish populations. These fish are affected in two ways. 



First, impoundments may be constructed so as to raise the 

 natural level of lakes. Superficially it would appear that such im- 

 poundments would be beneficial in that they would increase the size 

 of the lake and thus increase the size of the fish populations. Such 

 impoundments are constructed, however, for water use. The level of 

 the lake must fluctuate. If the fluctuations of the lake level amount 

 to only a few feet, the lake may well be quite satisfactory for fish 

 populations. 



Montana has excellent fishing in many impoundments of this 

 type. When the annual drawdown in the impoundments increased 

 to from 25 to 100 feet as is common in many Montana reservoirs, 

 it becomes impossible to maintain populations of fishes adequate 

 for angling. 



Second, dams may be constructed on streams tributary to lakes. 

 Trout, most important in Montana, do not normally reproduce in 

 lakes, but migrate out of the lakes and spawn in the tributaries. 

 Such dams may well eliminate important segments or all of the 

 spawning grounds upon which lake fish depend. Such has been the 

 case with Flathead Lake where Hungry Horse Dam has denied 

 many miles of valuable spawning grounds to the cutthroat and Dolly 

 Varden trout which annually move out of Flathead Lake. 



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