Summary 



In July and September 2002, periphyton samples were collected from 20 sites on 14 streams in 

 the Ruby River TMDL planning area in southwestern Montana for the purpose of assessing whether these 

 streams are water-quality limited and in need of TMDLs. The samples were collected following MDEQ 

 standard operating procedures, processed and analyzed using standard methods for periphyton, and 

 evaluated following modified USEPA rapid bioassessment protocols for wadeable streams. 



At the lower site on Coal Creek, a depressed pollution index and an elevated siltation index 

 indicated minor impairment from organic loading and sedimentation. Other than slight organic loading at 

 the upper site on Indian Creek, diatom metrics indicated excellent biological integrity, no impairment, 

 and full support of aquatic life uses at both sites on this stream. An elevated siltation index and a 

 depressed pollution index indicate moderate impairment from sedimentation and minor impairment from 

 organic loading in lower Ramshorn Creek. 



In addition to the natural stress evident in Currant Creek, this site exhibited minor impairment 

 from sedimentation. Other metrics indicated no impairment and excellent biological integrity. The lower 

 site on California Creek supported an exceptionally large number of motile diatoms for a mountain 

 stream, which indicated severe impairment from sedimentation. A slightly depressed pollution index 

 suggests minor impairment from organic loading at this site. Borderline values for the pollution index 

 and siltation index suggest minor impairment from organic loading and sedimentation in Harris Creek. 



Aside from a large number of Achnanthidium minutissimum and natural stress due to steep 

 gradients, coldwater temperatures and low nutrients, diatom metrics indicate good biological integrity in 

 Shovel Creek. Hawkeye Creek supported an exceptionally large number of motile diatoms for a 

 mountain stream, suggesting severe impairment from sedimentation. This site also had a slightly 

 depressed pollution index, indicating minor impairment from organic loading. An elevated number of 

 motile diatoms indicate minor impairment from sedimentation m Warm Springs Creek. One 

 teratological diatom valve was counted at this site. Otherwise, diatom metrics indicated excellent 

 biological integrity. 



Mill Gulch had excellent biological integrity for a mountain stream and diatom species richness 

 was exceptional (70 species counted). The lower site on Garden Creek supported an elevated number of 

 motile diatoms, indicating minor impairment from sedimentation. An elevated number of motile diatoms 

 in Mormon Creek indicate moderate impairment from sedimentation. A depressed pollution index also 

 indicates minor impairment from organic loading. A relatively large number of teratological diatoms 

 suggest that this site may have elevated concentrations of heavy metals. 



More than 13 percent of the diatoms in the North Fork of Greenhorn Creek were abnormal, 

 which suggests severe impairment from heavy metals. The number of motile diatoms here was also 

 elevated, indicating minor impairment from sedimentation. A large number of motile diatoms indicate 

 moderate impairment from sedimentation in the West Fork of the Ruby River. The pollution index was 

 also depressed here, indicating minor impairment from organic loading. 



