SUMMARY 



Composite periphyton samples were collected from natural 

 substrates at 17 sites on the Teton River and tributaries in the 

 summer of 1998. All but 6 of these samples were evaluated in an 

 earlier report (Bahls 1999) . This report evaluates the support 

 of aquatic life uses at the remaining 6 sites: 3 on the North 

 and South Forks and 3 on the mainstem of the Teton River. 



All 6 sites supported relatively small amounts of periphyton 

 growth. Insufficient numbers of diatoms were available in the 

 samples from the North and South Forks for conducting diatom 

 proportional counts, probably because of low nutrients. 



The site at the Gaging Station had good water quality and 

 only minor impairment. Increasing diatom species richness and 

 diversity values and decreasing pollution index values indicated 

 increasing nutrient enrichment between the lower site on the 

 North Fork and the site at Breen's above Choteau . 



Diatom metrics at the site near Collins indicated full 

 support of aquatic life uses when compared to criteria developed 

 for mountain streams, but only partial support and moderate 

 impairment when compared to criteria for prairie streams. The 

 probable causes of impairment here were siltation and nutrient 

 enrichment. 



The sites at Kelly Ranch and Dent Bridge had very similar 

 diatom floras and metrics that indicated moderate impairment and 

 partial support of aquatic life uses. These sites had very low 

 diatom diversity for prairie streams and were dominated by a 

 single species of free-living diatom. The probable causes of 

 impairment here were siltation and habitat homogeneity (lack of 

 habitat diversity) . 



