At Station 3, the epiphyte Chamaesiphon dominated the flora 

 in 1998 and rubbery dark-green colonial mats of Schizothrix 

 dominated in 1999. Different species of Chamaesiphon tolerate a 

 wide range of water quality conditions; most species of 

 Schizothrix are saprophobic, meaning that they are restricted to 

 very clean waters (VanLandingham 1982) . 



Three genera of filamentous green macroalgae were present in 

 the East Boulder River samples, although none of these algae were 

 abundant or conspicuous. Chaetophora, which is characteristic of 

 cold, rapidly flowing streams, was common at Station 3 in 1998. 

 Ulothrix, which also indicates cold, flowing waters, was frequent 

 at Stations 1, 2 and 3 (1999 only) . Stigeoclonium, which 

 sometimes indicates nitrogen enrichment, was frequent at Station 

 3 in 1998 and common at Stations 1, 3 (in 1999) and 5. 



DIATOMS 



The major diatom species in the East Boulder River were 

 either sensitive to pollution (Class 3) or only somewhat tolerant 

 of pollution (Class 2) . Achnanthes minutissima was the dominant 

 diatom species in the upper East Boulder River, accounting for 

 over 50% of the diatom cells at Stations 1 and 2 (Table 5) . This 

 is a pioneer "weed" species that colonizes recently disturbed 

 substrates. In the East Boulder River, the disturbance 

 registered by large numbers of this diatom is probably natural 

 and due to physical scour caused by high current velocities. 

 Percentages of A. minutissima approaching 70% have been recorded 

 in pristine streams in western Montana (Bahls et al . 1982) . 



Cold, fast, nutrient-poor waters and large numbers of 

 Achnanthes minutissima were also responsible for the very low 

 species richness and species diversity values in the upper East 

 Boulder River (Table 5) . Rather than indicating minor to 

 moderate impairment, the abundance of A. minutissima and the low 



