biological integrity of any of the sites in this study. 



Water quality and biological integrity remained good at all 

 of the downstream sites in the Redwater River. Minor impairment 

 was indicated by some organic loading and by an occasional 

 deformed cell or a slightly elevated percent dominant species 

 value. Diatom diversity remained high all the way to the mouth 

 of the Redwater and the siltation index was within acceptable 

 limits for prairie streams (Table 5) . 



East Redwater River 



The East Redwater River fully supported its aquatic life 

 uses. Minor impairment was indicated by some organic loading and 

 by a slightly elevated percent dominant species value (34.5%). 

 The dominant diatom species here was Thalassiosira pseudonana, a 

 quasi-planktonic centric diatom that is common in eastern Montana 

 streams (Bahls, unpublished data) . The East Redwater had 

 slightly more than half of its flora in common with the site on 

 the Redwater below their confluence (RW3-F) , indicating that it 

 had a significant influence on the biota and water quality in the 

 main Redwater River. 



QUALITY ASSURANCE 



Both analysts found four common algal genera in the sample 

 from below the Circle STP (Appendix B-1) . Diatoms were rated as 

 very abundant and ranked second in volume by both analysts. The 

 dominant ^enus in the sample was identified as Enteromorpha by 

 Hannaea and as Schizoweris by PhycoLogic. These two genera are 

 closely related and have similar water quality preferences 

 (Prescott 1978, Smith 1950) . 



Both analysts identified Diatoina tenue as the dominant 

 diatom in replicate slides prepared from the periphyton sample 

 collected below the Circle STP (Appendix B-2) . Diatom metrics 

 generated from the replicate counts were very close. However, 

 the slightly larger percent abundance of the dominant diatom in 

 the slide counted by PhycoLogic resulted in a rating of severe 

 and nonsupport of uses at the site below the Circle STP. The _ 

 similarity index for these two replicate counts was 83.29, which 

 is acceptable. 



14 



