scraped, brushed, or sucked from natural substrates in proportion 



to the rank of those substrates at the study site. Macroalgae 

 were picked by hand in proportion to their abundance at the site. 

 All collections of microalgae and macroalgae were pooled into a 

 common container and preserved with Lugol's (IKI) solution. 



Samples were examined to estimate the relative abundance and 

 rank by biovolume of diatoms and genera of soft (non-diatom) 

 algae according to the method described in Bahls (1993) . Soft 

 algae were identified using Prescott (1978) , Smith (1950) , and 

 Whitford and Schumacher (1984) . These books also served as the 

 main references on the ecology of the soft algae. 



After the identification of soft algae, raw periphyton 

 samples were cleaned of organic matter using sulfuric acid, and 

 permanent diatom slides were prepared in a high refractive index 

 mounting medium following Standard Methods for the Examination of 

 Water and Wastewater (APHA 1998) . For each slide, between 400 

 and 441 diatom cells (800 to 882 valves) were counted at random 

 and identified to species. The following were used as the main 

 taxonomic and autecological references for the diatoms: Krammer 

 and Lange-Bertalot 1986, 1988, 1991a, 1991b; Patrick and Reimer 

 1966, 1975. Lowe (1974) was also used extensively as an 

 ecological reference for the diatoms. 



The diatom proportional counts were used to generate an 

 array of diatom association metrics (Table 2) . A metric is a 

 characteristic of the biota that changes in some predictable way 

 with increased human influence (Barbour et al . 1999) . 



Metric values from the Teton River were compared to numeric 

 biocriteria developed for Montana streams (Tables 3 and 4) . 

 These criteria are based on metric values measured in least- 

 impaired reference streams (Bahls et al . 1992) and on metric 

 values measured in streams that are known to be impaired by 



