Evidence of excessive algae growth in the upper Clark 

 Fork basin has been reported since 1974 (Casne et al. 1975). 

 Aerial surveys in 1973-74 showed dense growths of algae 

 occurring between Deer Lodge and the mouth of the Blackfoot 

 River. These growths were attributed in part to insufficient 

 streamflows during the spring months to scour the previous 

 year's algae growth. Very heavy growths of algae have 

 occurred again during the summers of 1984 to 1988, also 

 associated with periods of below-normal spring runoff. 



Several studies have been conducted in recent years to 

 describe and quantify algae growths in the river and to 

 define the factors contributing to them. Bahls (1987) has 

 described the species composition and species diversity for 

 composite algae samples taken in 1986 at 28 stations located 

 between Silver Bow Creek and the Idaho border. Cladophora 

 sp . was the most consistently abundant green algae with peak 

 occurrences in the reaches from Gold Creek to Missoula and 

 from Superior to the confluence of the Flathead River. 

 Excessive algae growths did not occur in Silver Bow Creek and 

 the Clark Fork above Deer Lodge, presumably due to metal 

 toxicity. Diatoms were the dominant algae at the Turah and 

 Harper Bridge stations. These sites were characterized by 

 low species diversity and a very small percentage of 

 pollution-tolerant species. In 1987, EPA (1987b) charac- 

 terized the abundance of algae attached to natural and 

 artificial substrates in the upper and lower river. 

 Chlorophyll and biomass were especially high in the upper 

 river stations. 



Increased algae growth occurred below the municipal 

 wastewater treatment plants and below the Champion Inter- 

 national discharge. Algal biomass and chlorophyll decreased 

 downstream from Champion's mill to the town of Plains (Ingman 

 1985) . 



Nuisance quantities of algae have not been reported in 

 the lower Clark Fork reservoirs. Water level fluctuations 

 and relatively rapid flushing rates in the reservoirs 

 probably prevent the establishment of nuisance-level algae 

 blooms or rooted aquatic macrophytes. 



Algae and macrophytes are a major concern in Lake Pend 

 Oreille, Idaho. In recent years, residents and recreation- 

 ists have reported an increase in littoral zone (near-shore) 

 algae and macrophytes (rooted aquatic plants) . A 1986 study 

 of periphyton growth in Lake Pend Oreille suggests that 

 eutrophication of the lake is accelerating (Falter and Kann 

 1987) . 



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