with increased human influence (Barbour et al . 1999) . 



Metric values for Big Dry Creek and Little Dry Creek were 

 compared to numeric biocriteria developed for streams in the 

 Great Plains Ecoregions of Montana (Table 3) . These criteria are 

 based on metric values measured in least- impaired reference 

 streams (Bahls et al . 1992) and on metric values measured in 

 streams that are known to be impaired by various sources and 

 causes of pollution (Bahls 1993) . 



The criteria in Table 3 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. 



Besides the ecoregional biocriteria listed in Table 3, 

 metrics for Big Dry Creek were also compared to metrics generated 

 from a local, least- impaired reference stream using Protocol II 

 in Bahls (1993) . Little Dry Creek was used as the local, least- 

 impaired reference stream. 



Protocol II is based on the percentage of change in metric 

 values at the study site(s) from values measured at the local 

 reference stream. Criteria for evaluating biological integrity 

 using Protocol II are given in Table 12 in Bahls (1993) . 



Protocol II may be used if a tributary stream is available 

 that fully supports its aquatic life uses, that is, if it has a 

 rating of "good" or "excellent" biological integrity using 

 Protocol I. Little Dry Creek exhibited only minor impairment 

 using Protocol I and thereby qualifies as a local reference site. 



