Summary 



In June 2003, periphyton samples were collected from two sites on Eagle Creek in the 

 Bulhvhacker-Dog TMDL planning area in north central Montana for the purpose of assessing 

 whether Eagle Creek is 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. 



Since Eagle Creek begins in a mountain ecoregion and ends in a prairie ecoregion, 

 diatom metrics generated from both samples were compared to criteria developed for both 

 mountain and plains streams. The upper site (below Highway 236) had good biological integrity 

 for a mountain stream and excellent biological integrity for a plains stream. The limiting factors 

 at this site were sedimentation and organic loading. The lower site (near mouth) had fair 

 biological integrity for a mountain stream and good biological integrity for a prairie stream. 

 Here also, the limiting factors were sedimentation and organic loading. 



The two sites had somewhat similar algal floras, indicating that only minor changes in 

 envirormiental conditions occurred between them. Both sites had excellent diatom species 

 richness, diversity, and equitability. The majority of diatoms at both sites indicated fresh, 

 alkaline, and reasonably well oxygenated waters. Both the diatoms and the major non-diatom 

 algae indicated a steady flow of cool water and elevated inorganic nutrients at both sites. There 

 were no indicators (e.g., abnormal diatoms) of toxic chemicals at either site. 



