irrigated lands of the Missouri valley. Although much of the 

 water eventually returns to the river channel, the waters have 

 been muddied and the water quality degraded. Irrigation 

 reservoirs impound numerous reaches of the main stems and their 

 tributaries. Several irrigation canals are so well established 

 that they have fisheries of their own, which were assessed in the 

 Montana Rivers Study. 



The Rocky Mountain Front drainages had the lowest number of 

 reaches with a final resource value of Class I or II when compared 

 to the other 11 drainage basins assessed in the state. No reaches 

 received a Class I or II in the sport fishery value and only 10 

 were rated a Class II or above in the habitat and species value 

 (Tables 43 and 44). Of these ten reaches, seven were located in 

 the Marias River drainage where pure or potentially pure 

 populations of westslope cutthroat trout reside in upper headwater 

 tributaries. Ninety percent of the 128 assessed reaches in 1,271 

 miles received a final resource value of Class III or less. Only 

 86 miles of the 466 main stem miles on the Marias, Teton, 

 Dearborn, and Sun received a Class II final resource value. 

 Because wilderness areas, national parks, and Indian reservations 

 were not assessed, much of the more pristine portions of the Rocky 

 Mountain Front river drainages were excluded from the study. 



The coldwater fisheries of the headwater streams of the Marias 

 River include native and exotic trout species and mottled sculpin. 

 Immediately below Tiber Reservoir, 76 miles above the mouth, a 

 tailwater fishery of rainbow and brown trout exists. Other game 

 species within this section include channel catfish, sauger, 

 shovelnose sturgeon, burbot and mountain whitefish. Although this 

 fishery attracts local attention, its Class II final resource 

 value was due to the presence of an occasional migrating 

 paddlefish. In years when spring runoff is of a sufficient 

 duration and magnitude, paddlefish migrate upstream from Fort Peck 

 Reservoir into the Marias, presumably to spawn. Missouri sauger 

 and shovelnose sturgeon also use the Marias for spawning. 



The natural fish habitat of the Teton has been significantly 

 altered by nine major floods since the late 1800s and an extensive 

 system of irrigation diversions. Irrigation withdrawals dewater 

 the river during the summer months. Of the three main stem reaches 

 totaling nearly 200 miles, only a 10-mile reach above Choteau 

 received a Class II habitat and species value for its high species 

 diversity. The remainder of the river received a Class III in 

 habitat and species, and a Class IV in the sport fisheries value. 



In the Sun River drainage, an irrigation canal from Pishkun 

 Reservoir received a Class III final resource value, which was as 

 high (and higher than the lower 18 miles of the main stem) as the 

 Sun River itself. The 38-mile Sunny Slope Canal provides a local 

 fishery of self-sustaining arctic grayling, which survive through 

 the winter in isolated pools after the water has been shut off. 



112 



