STUDY NUMBER ; 6.3 



ORGANIZATION : Environmental Protection Agency (EPS) 



TITLE OF STUDY ; Chronic Bioassays of Upper Clark Fork River 

 Water 



CONTACTS ; Dick Montgomery - EPA - 449-5486 



Loren Bahls - DHES, WQB - 444-2406 



OBJECTIVE ; Evaluate the toxicity of upper Clark Fork River 

 water to three life stages of rainbow trout. 



DURATION ; 1985 - ? 



CURRENT STATUS ; Flow-through bioassays were conducted with 

 rainbow trout green eggs, eyed eggs and fingerlings. Test 

 water was collected from the Clark Fork River near Deer 

 Lodge. Dilution water was obtained from Taylor Creek, a 

 nearby perennial stream. A two-bank dilution system was 

 utilized. Tests were conducted from May 7 through June 6, 

 1985. All tests were conducted at 10 + 2° C. The egg tests 

 were conducted for the full thirty days. Fingerling tests 

 were conducted for 13 days. 



The tests were timed to coincide with spring runoff, 

 when high concentrations of heavy metals are normally present 

 in the upper Clark Fork River. Normal spring runoff did not 

 occur during 1985 and resulting metal concentrations did not 

 produce significant mortalities in any of the tests. 



Rain events during the last half of the study produced 

 sharp, brief increases in metal concentrations. These 



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