k Some algae, such as the filamentous greens, are conspicuous 



and their excessive growth may be aesthetically displeasing, 

 deplete dissolved oxygen, interfere with fishing and fish 

 spawning, clog water filters and irrigation intakes, create 

 tastes and odors in drinking water, and cause other problems. 



PROJECT AREA AND SAMPLING SITES 



The project area is located in Lewis & Clark and Powell 

 Counties in western Montana. The surface geology of the upper 

 Blackfoot River watershed consists mostly of Precambrian Belt 

 Series rocks in the uplands and Quaternary basin fill in the 

 valleys (Renfro and Feray 1972) . 



The Blackfoot River heads near Rogers Pass (elevation 5,610 

 feet) north of Helena. Most tributaries arise at elevations 

 ranging from 5,000 to 9,000 feet. At 4,300 feet, the Blackfoot 

 ^ River above Nevada Creek is the lowest site in the study area. 

 Vegetation is mainly mixed conifer forest with alpine tundra on 

 the highest peaks and open parks of fescue grassland near the 

 mouth of Poorman Creek and near the mouth of Nevada Creek at the 

 lower end of the study area (USDA 1976) . 



The upper Blackfoot River watershed is within the Northern 

 Rockies Ecoregion of Montana (Woods et al . 1999). The main land 

 uses are recreation, livestock grazing, logging, and mining. The 

 Blackfoot River is popular for fishing and floating, mainly below 

 the study area. The upper Blackfoot River drainage has many 

 abandoned mine sites and a long history of hardrock mining. 



Periphyton samples were collected at 12 sites on the 

 Blackfoot River and four of its tributaries (Maps 1-7, Table 1). 

 Most sampling sites are on public (USPS, BLM, or State) land. 

 The Blackfoot River and its tributaries are classified B-1 in the 

 k Montana Surface Water Quality Standards. 



