The middle reach of the Clark Fork supports a fauna rich 

 in species compared to the impoverished upstream fauna (Shinn 

 1970; McGuire 1987). Spindler (1959), Averett (1961), Shinn 

 (1970) and McGuire (1987) have reported more diverse faunas 

 below Missoula than above. Organic wastes from the Missoula 

 Wastewater Treatment Plant (WWTP) , Stone Container Corpora- 

 tion's pulp mill, and upstream sources have been the pol- 

 lutants of historical concern in this river reach (Watson 

 1985) . The Missoula WWTP is the largest point source of 

 nutrients in the drainage and, until secondary treatment was 

 installed in 1978, probably had the greatest potential for 

 creating toxic conditions in the Clark Fork downstream from 

 Milltown Dam. Shinn 's study indicated a sharp decline in 

 species richness immediately below the Missoula WWTP outfall 

 compared with stations just upstream and farther downstream, 

 although species richness was still greater than in the 

 headwaters . 



The Institute of Paper Chemistry (IPC) began an annual 

 biological assessment of environmental conditions near the 

 Stone Container Corporation's (Frenchtown) mill in 1956 to 

 detect impacts from the mill's effluent and settling pond 

 seepage (IPC 1957-1984). During the mill's first year of 

 operation (1958-59) , the untreated effluent had a significant 

 localized impact on the fauna. Spindler and Whitney (1960) 

 documented a fish kill and a shift in the composition of the 

 benthic community, while the IPC (1962) found reduced 

 densities of sensitive insect species and reduced species 

 richness below the mill outfall. The subsequent recovery of 

 the benthic community was documented (IPC 1962) when effluent 

 treatment was initiated a year later. Other than the 

 deleterious effects during the first year of operation, the 

 paper mill has generally had minor impacts on the Clark Fork. 

 During the 1960s, slight reductions in species richness were 

 sometimes noted near the effluent outfall, and organic 

 enrichment was documented immediately downstream. Wastewater 

 treatment at the mill has been improved several times, and 

 since 1975, impacts have been limited to nutrient enrichment 

 (Rades 1985) . 



While the IPC studies were designed to detect impacts 

 from a single point source, they also provide valuable 

 information for evaluating overall environmental conditions 

 in the river between Missoula and Alberton. Although the IPC 

 annual reports did not usually address environmental 

 stresses, they did show some evidence of stresses throughout 

 the study area. For instance, in 1959, 1963, 1964, 1967, 

 1974, and 1975, reduced macroinvertebrate densities, species 

 richness, and/or shifts in relative abundance were evident at 

 most stations. Perturbations at IPC control sites appeared 

 greatest during high runoff years and, therefore, may have 

 resulted from elevated heavy metals concentrations during 



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