(86.5%) at SbrC-02 and the resulting low diversity index (0.96) 

 both indicate severe impairment and nonsupport of uses. 



The two sites on Sandbar Creek shared only about a quarter 

 of their diatom floras (Table 7) . This indicates that a moderate 

 amount of environmental change (impairment) occurred between the 

 two sites. 



Willow Creek. Willow Creek was the only one of the study 

 streams where diatoms indicated that both sites suffered only 

 minor impairment and fully supported their aquatic life uses 



(Table 7) . The upstream site (WilC-Ol) had a slightly elevated 

 siltation index and a few abnormal diatom valves. The lower site 



(WilC-02) had somewhat depressed pollution index, indicating some 

 organic loading. This organic loading may be natural and due to 

 the swampy nature of this stream. 



Both sites supported relatively large numbers of small, 

 free-living Fragilariaceae {Fragilaria vaucheriae, Staurosira 

 construens , Synedra rumpens) (Table 7) . These diatoms indicate 

 highly stable stream flows and reflect the low gradient and 

 stable flows of Willow Creek. The two sites on Willow Creek had 

 almost half of their diatom floras in common, indicating only 

 minor environmental change occurred between them. 



Both sites on Willow Creek supported a few abnormal diatom 

 valves (Table 7) but these sites had two of the three lowest 

 percentages of abnormal valves of all the sites in the study area 

 (Figure 1) . The upper Blackfoot River and the tributaries 

 sampled for this study are unusual in that abnormal valves were 

 recorded at all study sites (Figure 1) . This probably indicates 

 the influence of elevated heavy metals in these waters. 



14 



