runoff. Conversely, during years when runoff was relatively 

 low (e.g. 1966, 1969, 1973, and 1977), investigators 

 typically noted indications of nutrient enrichment (increased 

 macro invertebrate densities and biomass) at sites upstream 

 and downstream from the paper mill. These findings suggest 

 that biologically significant heavy metals contamination has 

 occurred in the Clark Fork below the Milltown Dam during high 

 runoff years, and it occasionally has extended downstream at 

 least as far as Alberton. 



Confluence of the Flathead River to the Idaho Border 



Because scant data are available for the Clark Fork 

 downstream of its confluence with the Flathead River, only a 

 few generalizations regarding environmental conditions in the 

 lower river can be made. Heavy metals contamination does not 

 appear to have been a problem in this reach of the Clark 

 Fork in recent years. Hornig and Hornig (1985) and McGuire 

 (1987) reported increased abundances of several mayfly and 

 mollusk species considered intolerant of heavy metals below 

 the confluence of the Flathead River. The benthic com- 

 munities described in these studies suggest that nutrient 

 enrichment is not a serious problem at this time. Stream 

 regulation, particularly fluctuating flows, appears to be the 

 most limiting factor to maximum benthic production in the 

 lower Clark Fork. 



FISHERIES 



Introduction 



The fishery in the Clark Fork has passed through many 

 stages in the past 140 years. Beginning as a varied and 

 productive fishery, it was devastated by human activities in 

 the watershed. Now it is a slowly recovering system. 

 Although the Clark Fork fishery today is greatly improved 

 over what it was just a few decades ago, its recovery has 

 been erratic, and the fishery is considered to be far below 

 the carrying capacity of the river. 



In recent years, the DFWP has initiated several 

 investigations to determine why the Clark Fork fishery is 

 poor relative to other rivers of comparable size, such as the 

 Blackfoot River. Information that has been obtained includes 

 population estimates, spawning ground surveys, recruitment, 

 bioassays, and fish stocking survival. In 1987, the DFWP 

 intensified its efforts to obtain information needed to 

 guide management decisions. 



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