All tributary flows are probably significant in 

 improving water quality but increases in trout abundance 

 appear to be significant only below the mouth of Rock Creek. 



Fish kills have been observed frequently in the upper 

 Clark Fork over the last several years. State agencies have 

 documented kills that occurred on August 9, 1983; August 1, 

 1984; June 18, 1987; July 3, 1987; and May 27, 1988. All 

 five kills were associated with thunderstorms and are 

 believed to be a result of metals entering the river due to 

 rainfall on streamside mine tailings. Although documentation 

 has been more thorough for some kills than for others, it has 

 included photographs of red water immediately after storms, 

 water samples indicating that a slug of metals entered the 

 stream during the storm, high concentrations of metals 

 (particularly copper) in the gills of fish that were killed, 

 extremely high concentrations of metals in pools of water 

 adjacent to the stream, and other subjective evidence 

 pointing to the conclusion that the fish were killed by 

 metals (Department of Fish, Wildlife and Parks files) . 



In response to concerns that tailings present in the 

 Mill-Willow Bypass have been the origin of several fish 

 kills, the Anaconda Minerals Company is currently modifying 

 the bypass to divert water from the upper portions of the 

 bypass into the Warm Springs Ponds during summer. This 

 change is expected to isolate some of the more immediate 

 sources of metals from the upper river but will not entirely 

 eliminate the possibility of tailings entering the river 

 during thunderstorms. 



High concentrations of metals are also present in the 

 river during spring runoff. No documentation shows that 

 metals present in the river during spring runoff kill adult 

 trout. However, metals present during runoff events are 

 believed to chronically stress populations and may cause 

 acute toxicity, especially to sensitive, early life stages. 

 Such occurrences could easily go unnoticed. Many biologists 

 also believe that the absence of rainbow trout from much of 

 the upper river is due to their lower tolerance to metals 

 than brown trout. 



Several investigators have evaluated the toxicity of 

 river water in the Clark Fork drainage (Table 3-29) . 

 Bionomics (1979) tested the toxicity of water discharged from 

 Warm Springs Pond 2 to early life stages of rainbow trout 

 (eggs and fry) and to Daphnia middendorf f iana . which is a 

 native daphnid, or water flea. water, but all fry, 

 including those exposed to dilutions of 50 and 7 5 percent 

 pond water, experienced reduced growth. Copper and zinc 

 concentrations in a 50 percent dilution of pond 2 water 

 averaged 25 and 65 ug/1, respectively. Additionally, Daphnia 



3-114 



