McDonald Creek and the five upstream sites on the Teton 

 River may be considered mountain streams for the purpose of 

 periphyton assessment, and metrics from these sites will be 

 compared to criteria in Table 3 . These sites are described in 

 the Montana Surface Water Quality Standards as supporting cold- 

 water or transitional (cool-water) fisheries (Table 1) . 



The lower four sites on the Teton River may be considered as 

 prairie streams, and metrics from these sites will be compared to 

 criteria in Table 4. These sites are classified as supporting 

 warm-water fish and associated aquatic life (Table 1) . Because 

 of the transitional nature of the Teton River in the vicinity of 

 Highway 221, metrics from this station will be evaluated using 

 criteria for both mountain streams and prairie streams (Tables 3 

 and 4) . 



In some cases, natural stressors (e.g., high gradient, low 

 light, cold temperatures, low nutrients) can mimic the effects of Hp 

 man-caused impairment on these metrics. An experienced 

 phycologist with some knowledge of the study stream can usually 

 sort out the natural stressors from the man-made ones . 



The criteria in Tables 3 and 4 distinguish among four levels 

 of impairment and three levels of aquatic life use support: no 

 impairment or only minor impairment (full support) ; moderate 

 impairment (partial support) ; and severe impairment (nonsupport) . 

 These impairment levels correspond to excellent, good, fair, and 

 poor biological integrity, respectively. 



Only periphyton samples collected in summer (June 21- 

 September 21) can be compared to reference stream samples because 

 metric values change seasonally and summer is the season in which 

 reference streams were sampled for biocriteria development. 



