cyanobacteria, although none were found in the sample. 



The non-diatom algae from these sites indicated cold, fast- 

 flowing waters and low concentrations of dissolved nutrients. 

 Algal standing crops were evidently very small, especially at 

 Cottonwood Creek Station 1. 



DIATOMS 



Diatom association metrics indicated good to excellent 

 biological integrity at all of the sampling sites (Table 5) . 



Most of the major diatom species in Cottonwood Creek and 

 Rock Creek were sensitive to or only somewhat tolerant of 

 pollution (Table 5) . Nitzschia palea, a nitrogen indicator and 

 a diatom that is quite tolerant of pollution, was a major species 

 only at Cottonwood Creek Station 2, where it accounted for 5.25% 

 of the cells. The pollution index at this site was borderline 

 and indicated minor impairment from organic loading but full 

 support of aquatic life uses. The siltation index was also 

 borderline at this site, but well within the range of good 

 biological integrity. 



Rock Creek Station 1 had somewhat depressed species richness 

 and species diversity values, indicating minor stress (Table 5) . 

 This stress was likely natural in origin and due to the cold and 

 nutrient-poor water at this site. The pollution index at this 

 site was on the threshold of minor impairment due to the large 

 percentage of cells in the species Gomphonema angustatum. This 

 taxon prefers small, cold-water streams (Krammer & Lange-Bertalot 

 1986) and oligotrophic to somewhat mesotrophic water (Patrick and 

 Reimer 1975) . Although it is somewhat tolerant of pollution 

 (Lange-Bertalot 1979) , it is also found in nutrient-poor waters. 



