SUMMARY 



Composite periphyton samples were collected at two sites on 

 McDonald Creek and at nine sites on the Teton River in July and 

 August 1998. The samples were analyzed using standard methods 

 for the rapid bioassessment of stream periphyton. 



McDonald Creek had a very rich algal flora that reflected 

 the lacustrine origin of this stream in the Pine Butte Swamp 

 Preserve. Despite severe dewatering at the lower station on 

 McDonald Creek, water quality and biological integrity remained 

 excellent. Aquatic life uses would be fully supported in 

 McDonald Creek if streamflows are restored. 



Sites on the upper Teton River (above Highway 221) had good 

 water quality and biological integrity. Severe dewatering at 

 Breen's, eroding streambanks and sediment from Deep Creek, and 

 discharges from the Choteau WWTP and Priest Butte Lakes all had 

 only minor effects on the periphyton community. As with McDonald 

 Creek, restoring streamflows to the upper Teton River during the 

 irrigation season would likely result in the full support of 

 aquatic life uses. The North Fork of the Teton River proved to 

 be a suitable reference stream for periphyton. 



Floristic richness and biological integrity decreased 

 significantly below Highway 221 in the lower Teton River. 

 Sedimentation and habitat homogeneity resulting from channel 

 instability were likely responsible for the observed decline in 

 periphyton biointegrity in this reach of the river. Periphyton 

 metrics at Dent Bridge indicated moderate impairment with only 

 partial support at this site. Dent Bridge was the only site on 

 either McDonald Creek or the Teton River where periphyton metrics 

 indicated less than full support of aquatic life uses. 



