other Water Uses 



Other water users in the Clark Fork Basin also cause 

 individual as well as cumulative impacts on streamflows. In 

 the upper basin, the main Clark Fork and most of its tribu- 

 taries are affected by irrigation diversions. Warm Springs 

 Creek, the Little Blackfoot River, and Flint Creek are major 

 tributaries with fisheries affected by diversions. Portions 

 of the Clark Fork above Deer Lodge suffer from extreme 

 dewatering, as do most of the smaller tributaries, such as 

 Lost, Rock, Dempsey, and Racetrack creeks. These streams all 

 provide fishing for trout, but their potential is limited by 

 reduced flows for irrigation. 



The Clark Fork downstream of Drummond shows the effects 

 of dewatering to a lesser extent than upstream reaches 

 (tributaries excluded) because there is less irrigated land 

 downstream of Drummond relative to the water supply. Hence, 

 the effects of dewatering are less apparent. 



The dewatering problems occur in July and August in most 

 years but begin earlier or last longer in dry years. Nearly 

 all diversions are for agricultural use. 



Dewatered streams occur because of the cumulative 

 effects of both old and new water rights. Many rights have 

 priority dates before the turn of the century. Since 1973, 

 when Montana implemented the new water law, water users have 

 had to apply for and be issued a permit to appropriate water. 

 Practically all permits in the basin are issued with few 

 conditions that will help the dewatering problem. 



The effects of dewatering streams with fish populations 

 are all generally the same — loss of physical habitat, higher 

 water temperatures, lower food production, and decreased 

 dissolved oxygen. The extent of these impacts depends on the 

 degree of dewatering and the local conditions within the 

 stream, the most severe being actual loss of a fish popula- 

 tion when a stream stops flowing. 



Fishing opportunities are reduced, aesthetic qualities 

 are poorer, and floating (where the stream is large enough) 

 becomes difficult or impossible when insufficient flows 

 occur, resulting in fewer recreational opportunities. 



Instream flows are a partial solution to the dewatering 

 problem. However, because instream flow rights cannot affect 

 senior diversionary water rights, they only preserve the 

 status quo of stream depletion. The rights do not prevent 

 dewatering, but can reduce future demands on the streams once 

 they are acquired. Rewatering of streams that have severe 

 flow problems can only be accomplished through new 



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