discharge would be reduced to accommodate the reduction in 

 dilution water of the receiving stream. However, adjusting 

 wastewater discharges in permits in response to chronic low- 

 flow conditions would be a slow process and would rely on 

 accurate, long-term stream discharge measurements for 

 calculating 7-day, 10-year low flows. 



It is important to recognize that industrial and 

 municipal wastewater discharge permits do not provide water 

 rights. Water use permits allow diversion and consumption of 

 water without regard to impacts on water quality. (An 

 exception is for large diversions for which the applicant 

 must show compliance with specific public interest criteria.) 



Reduced streamflows during the normal low-flow period 

 can affect the quality of water that is necessary to sustain 

 aquatic organisms. Other possible consequences of this 

 lowered streamflow are higher water temperatures, increased 

 amounts of dissolved solids, increased nutrient concentra- 

 tions, and lower dissolved oxygen levels. Reduced stream- 

 flows seasonally limit the ability of the Clark Fork to 

 assimilate its present pollution load. A reduction in 

 tributary streamflows will reduce the current capability of 

 tributary streams to discharge clean water into the Clark 

 Fork for dilution of pollutants. 



An instream flow reservation can help to prevent the 

 further deterioration of water quality during low-flow 

 periods. A reservation can also help to provide adequate 

 flows for enhanced aquatic populations that may occur in the 

 future as existing pollution problems are reduced or, 

 hopefully, eliminated. 



Water Supplv 



Instream flows in the Clark Fork Basin are also 

 important from a water supply standpoint, particularly in the 

 Missoula area. The Clark Fork provides about 46 percent of, 

 the annual recharge to the Missoula Aquifer, which is the 

 major source of drinking water for the Missoula area. It 

 also supplies water to over 30 small community water systems 

 and to several industrial users. An estimated 65,000 of 

 Missoula County's 77,400 residents use water from the 

 Missoula Aquifer (Missoula City-County Health Department 

 1987) . Therefore, maintaining adequate instream flows in the 

 Clark Fork is crucial to these residents and to others in the 

 basin who derive their water from aquifers recharged by the 

 river. 



3-19 



