V. 



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) . The Judith River heads in 

 the Little Belt Mountains (maximum elevation 9,175 feet) and 

 flows northeast for about 100 miles to where it enters the 

 Missouri River near the town of Winifred (pop. 162) . The two 

 sampling sites addressed in this report bracket a 10-mile-long 

 segment of the Judith River located between Ross Fork and Ware 

 northwest of Lewistown. 



The upper watershed of the Judith River lies within the 

 Northern Rockies Ecoregion (Woods et al . 1999) . The river then 

 traverses a band of the Montana Valley and Foothill Prairies 

 Ecoregion. The lower (and the longest) segment of the river--a 

 portion of which is addressed in this report- -flows through the 

 Northwestern Great Plains Ecoregion. 



The surface geology of the watershed is composed of Madison 

 Limestone in the mountainous headwaters and Colorado Shale 

 overlain by Quaternary gravel deposits at lower elevations 

 (Renfro and Feray 1972) . Vegetation is mixed forest in the 

 headwaters and mixed grassland at lower elevations (USDA 1976) . 



Periphyton samples were collected at two sites on August 9, 

 2000 (Table 1) . The upper site (J 1) is located west of Ross 

 Fork at an elevation of about 3,750 feet (Map 1) . The lower site 

 (J 3) is located east of Ware at an elevation of 3,450 feet (Map 



