SUMMARY 



In late May 1999, composite periphyton samples were 

 collected from natural substrates at 8 sites on the Redwater 

 River and 1 site each on Little Dry Creek and the East Redwater 

 River in eastern Montana. Samples were collected following DEQ 

 standard operating procedures, processed and analyzed using 

 standard methods for periphyton, and evaluated following modified 

 USEPA rapid bioassessment protocols for wadeable streams. 



The benthic algal flora indicated elevated salinity and 

 organic loading in the headwaters of the Redwater River, causing 

 moderate impairment and partial support of aquatic life uses at 

 the uppermost site (Gackle) . Salinity and organic loading 

 decreased downstream to Circle., Below the Circle STP, an 

 increase in organic and inorganic nutrients (but not salts) again 

 caused moderate impairment with partial support of aquatic life 

 uses'. Deformed diatoms below Circle also indicated the possible 

 presence of toxins in the water. 



Recovery was complete in the next 15 miles of stream. A 

 peak in the number of cells in the diatom family Epithemiaceae 

 indicated a low N:P ratio below Bluff Creek. Aquatic life uses 

 were fully supported from Bluff Creek downstream to Nickwall 

 Crossing near the mouth of the Redwater. 



Both Little Dry Creek and the East Redwater River fully 

 supported aquatic life uses with minor impairment from organic 

 loading and elevated nutrients. All of the sites on the Redwater 

 River also exhibited at least minor impairment from organic 

 loading and elevated nutrients. This may be the normal 

 background condition for streams in this area. 



