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 Fergus County near the city 

 of Lewistown, Montana (pop. 6,368). Cottonwood Creek heads in 

 the Big Snowy Mountains (maximum elevation 8,730 feet) and flows 

 northwest for about 30 miles to where it enters Big Spring Creek 

 near Hanover northwest of Lewistown. 



Cottonwood Creek begins in the Northern Rockies Ecoregion 

 but flows for most of its length through the Montana Valley and 

 Foothill Prairies Ecoregion (Woods et al . 1999). All three 

 sampling sites are within the prairie ecoregion. 



The surface geology of the Cottonwood Creek watershed 

 consists of Big Snowy dolomite and limestone in the headwaters, 

 metamorphic rocks of the Kootenai Formation in the middle reach, 

 and shales of the Colorado Group in the lower reach (Renfro and 

 Feray 1972) . Vegetation is alpine tundra and spruce-fir forest 

 in the headwaters, mixed forest and grassland in the middle 

 reach, and mixed grassland at lower elevations (USDA 1976) . 



Periphyton samples were collected at three sites on August 

 21, 2001. The upper site (M22CTWDC01) is located about 2 miles, 

 below the Cottonwood School at an elevation of 4,454 feet (Map 

 1) . The middle site (M22CTWDC02) is located below Beaver Creek 

 at an elevation of about 3,900 (Map 2) . The lower site 

 (M22CTWDC03) is located just above the confluence with Big Spring 

 Creek near Hanover at an elevation of 3,700 feet (Map 2) . 



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