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 (pop. 6,368) in central Montana. The Big Springs, 

 seven miles southeast of Lewistown, generate most of the 

 streamflow in Big Spring Creek. From Big Springs, Big Spring 

 Creek flows northwesterly for about 30 miles through Lewistown 

 and on to its confluence with the Judith River. 



Major tributaries of Big Spring Creek, including aquifers 

 feeding the Big Springs, head in the Big Snowy Mountains (maximum 

 elevation 8,730 feet), an outlier of the Northern Rockies 

 Ecoregion (Woods et al . 1999) . Although the segment of Big 

 Spring Creek addressed here is located in the Montana Valley and 

 Foothill Prairies Ecoregion, water quality is dominated by the 

 Big Springs. In the Montana Surface Water Quality Standards, the 

 stream is classified B-l above Lewistown and B-2 below Lewistown. 



The surface geology of the Big Spring 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 2 sites on May 25 and 

 at another 4 sites on August 20 and 22, 2001. The 2 sites 



