riffles would freeze during the winter. Approximately 650,000 m^ (7 million ft^) 

 of potential spawning habitat would be lost during the spring downstream from the 

 T&Y Diversion. During run-off, no flow would be present about one-third of 

 the time. Paddlefish would be unable to migrate upstream about one-fourth of 

 the years in which there would be measurable flow. With these flow levels, 

 there would be a minimal fishery downstream from the T&Y Diversion. 



With the high projection, flows would be almost nonexistent downstream from 

 the T&Y Diversion, and impacts would be extreme. 



Since that portion of the river downstream from the T&Y Diversion pro- 

 vides a spawning and nursery area for fish from the Yellowstone River, a 

 reduction in flows would also adversely affect the Yellowstone River fish 

 population. Thus, impacts on the Yellowstone River fishery as well as on the 

 Tongue River fishery would occur from reduced flow in the Tongue. 



IMPACTS ON WATER QUALITY 



The impacts of reduced flow on water quality were evaluated in terms of 

 total dissolved solids (TDS) concentrations (salinity). Concentrations of 

 TDS ranging from 670 milligrams per liter (mg/1 ) to a maximum of 1350 mg/1 

 were considered the range for a good, mixed fishery in western alkaline 

 streams (Klarich 1977). Some minor adverse effects would be expected at 

 concentrations over 670 mg/1, becoming more severe as concentrations 

 approached and exceeded 1350 mg/1. Therefore, TDS levels greater than 

 700 mg/1 were considered to have an impact on the fishery. 



Fall 



Four months (August-November) would have TDS greater than 700 mg/1 with 

 the low level of development. August levels could be high enough to deter 

 channel catfish migrations. With the intermediate level of development, all 

 months would be greater than 700 mg/1 ; August through December would be 

 greater than 1,000 mg/1. Channel catfish migration and spawning in August 

 could be affected. All months would show levels greater than 1,000 mg/1 

 with high development. Impacts would be the same as with intermediate 

 development. 



Winter 



December and January would have TDS concentrations greater than 700 mg/1 

 with low development, and all winter months (December-February) would have 

 greater than 700 mg/1 with intermediate development. December showed con- 

 centrations greater than 1,000 mg/1 under both intermediate and high development. 

 However, impacts should not be significant during this period. 



Spring 



No impact would be expected with low or intermediate development. Under 

 high development, March and April show TDS concentrations greater than 700 mg/1, 

 which could affect sauger migration and spawning. 



71 



