Brown trout, rainbow trout, brook trout and mountain 

 whitefish are the dominant sport fish in reach #2. Other 

 fish present include cutthroat trout, white sucker, longnose 

 sucker, mountain sucker, mottled sculpin and longnose dace. 



Cross-sectional measurements in reach #2 were made in a 

 624-ft subreach located near Gallatin Gateway at river mile 

 44. Seven cross-sections were placed in a riffle-pool se- 

 quence (Figures 12, 13 and 14). 



Big Hole River 



The free-flowing Big Hole River originates in the Bitter- 

 root Mountains of southwest Montana and flows 156 miles before 

 joining the Beaverhead River to form the Jefferson River 

 (Figure 15) . The river drains an area of approximately 

 2,476 square miles. Throughout its length, cattle ranches 

 and irrigated hay lands occupy much of the river valley. 

 During low water years, the dewatering of the river for the 

 irrigation of hay crops can be severe. 



Water quality throughout the river can generally be de- 

 scribed as excellent. The river has a calcium-bicarbonate 

 type water with low turbidity and low sulfate, sodium, 

 chloride and metals concentrations. Selected chemical prop- 

 erties of the river near Twin Bridges in 1977 and 1978 are 

 given in Table 4. Water temperatures considered undesirably 

 high for the growth and propagation of salmonids have been 

 recorded downstream of the USGS gage near Melrose in past 

 years when severe dewatering has occurred. 



Table 4. Selected chemical properties of the Big Hole River 

 near Twin Bridges, Montana in summer and fall, 

 1977 and spring, 1978 (data from Bahls et al., 

 1979) . 



Summer Fall Spring Mean 



Specific Conductance 



(umhos @ 25 C) 271 



Total Alkalinity 



(mg/1 CaC03) 



Phosphate (PO4 as P in mg/1) 

 Total Phosphorous (P in mg/1) 

 Nitrate plus Nitrite 



(NO3+NO2 as N in mg/1) 

 Ammonia (NH3 as N in mg/1) 

 Kjeldahl Nitrogen (N in mg/1) 



20 



