Summary 



In September 2004, pcriphyton samples were collected from two sites on Lake Creek in 

 the Upper Missouri-Dearborn TMDL Planning Area for the purpose of assessing whether this 

 stream 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 

 periphvton, and evaluated following modified USEPA rapid bioassessment protocols for 

 wadeable streams. 



Diatom metrics indicate impairment at both sites from sedimentation and organic loading. 

 Although impairment from sedimentation was moderate at the upstream site and minor at the 

 downstream site, the downstream site supported a larger percentage of highly motile diatoms, 

 suggesting that this site had more unstable substrates. Diatoms also indicate higher levels of 

 dissolved solids and organic nitrogen at the downstream site. Diatoms at both sites indicate 

 alkaline and eutrophic waters with 25 - 70% dissolved oxygen saturation and 4-13 mg/L BOD5. 



Conspicuous macroalgae were absent at the upstream site, whereas at the downstream 

 site the filamentous green algae Rhizocloniiiin and Schizomeris were abundant and common, 

 respectively. Rhizocloniiim is a common nuisance alga in streams of the western United States. 

 Schizomeris is most common in eutrophic waters, including waters below discharges from 

 sewage treatment plants. 



