INTRODUCTION 



This report evaluates the support of aquatic life uses, and 

 probable causes of impairment to those uses, in the upper Boulder 

 River (Yellowstone River Drainage) of southcentral Montana. This 

 report is based on the composition and structure of benthic 

 diatom associations included in 7 periphyton samples that were 

 collected at 4 sites on the river in 1991, 1992 and 1993. 



Beginning in the summer of 1991, the Water Quality Division 

 of the Montana Department of Health and Environmental Sciences 

 (now MDEQ) began receiving complaints from local residents about 

 excessive algae growth in the Boulder River. This algae growth 

 was considered an aesthetic nuisance and reported to be fouling 

 fishing lines and making wading difficult. Concern was expressed 

 that the dense algae growth may be affecting fish numbers, fish 

 growth, and associated aquatic life. 



In response to these concerns, MDHES conducted a study of 

 nutrients and algae in the Boulder River. The 7 samples that are 

 assessed here were collected in response to Boulder River algae 

 complaints and were first evaluated in the Boulder River nutrient 

 and algae report (Levine 1996) using metrics and bioassessment 

 protocols that were available at the time. 



However, additional metrics have since been added for 

 assessing use support, and the reference site protocol used in 

 1996 (Protocol II) was probably inappropriate for this study. 

 Hence, a reassessment of the existing Boulder River diatom data 

 (this report) was determined to be necessary (Pat Newby, MDEQ, 

 personal communication) . 



