4fc Oscillatoria. Amphithrix, a cyanophyte that prefers cool waters, was common at the upper site 

 but absent from the lower site. 



Mormon Creek. An occasional diatom and filament of Cladophora were the only algae 

 found in the sample from Mormon Creek (Table 3). 



North Fork Greenhorn Creek. Diatoms ranked first in biovolume, followed by three 

 genera of green algae and the red alga Aadouinella, which indicates cool water temperatures. 



West Fork Ruby River. Besides diatoms, which were abundant and ranked first in 

 biovolume, this site supported 7 genera of algae, including green algae, blue-green algae, and the 

 red alga Audoninel la (Table 3). 



Diatoms 



All of the major diatom species from the Ruby River TMDL planning area are included 

 in pollution tolerance classes 3 and 2, and are either sensitive to organic pollution or only 

 somewhat tolerant of organic pollution (Table 4). None of the major diatom species are most 

 tolerant of organic pollution (pollution tolerance class = 1). 



Stresses indicated at some of the sites appear to be natural in origin. For example, high 

 values for the disturbance index and percent dominant species in upper Ramshom Creek and 

 Shovel Creek indicate moderate stress related to steep gradients, fast currents, cold temperatures, 

 and low nutrient concentrations. High values for the pollution index and low values for the 

 siltation index and percent abnormal cells indicate that organic enrichment, sedimentation, and 

 toxic metals did not have a significant effect on the benthic algae at these sites (Table 4). Lower 

 but still elevated values for the disturbance index and percent dominant species indicate minor 

 natural stress in Currant Creek, upper California Creek, Harris Creek, and upper Garden Creek. 



Coal Creek. The dominant diatom species in upper Coal Creek was Epithemia sorex 



B ( 1 able 4). ( !ells of this diatom harbor nitrogen-fixing hlue-green algae as endosymbionts. Along 



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