Tributaries. Tributaries of 0' Fallon Creek supported 

 between 6 and 13 genera of non-diatom algae (Table 5) . The 

 average number of non-diatom algal genera reported from plains 

 streams in Montana is 13, with a range of 9 to 19 (Bahls 1993) . 

 Although six divisions of non-diatom algae were represented in 

 tributary samples, only green algae and cyanobacteria accounted 

 for a significant number of genera and algal cells (Table 5) . 



Diatoms and filamentous green algae ranked first or second 

 in biovolume at all tributary sites (Tabic 5) . Among green 

 algae, Rhizoclonium, Microspora, Oedogonium, and Chara accounted 

 for most of the biomass at tributary sites. The cool -water green 

 alga Microspora was present (and abundant) only at the upper site 

 on Sandstone Creek (AS-2) . The cool -water chrysophyte Tribonema 

 was found only at the upper site on Pennel Creek (DF-6) . The 

 macroalga Chara was found only in Pennel Creek. 



Euglenoid algae were present but uncommon at all but two 

 sites (DF-10 and AS-2) . Stigeoclonium, another indicator of 

 organic pollution, was present at AS-5. Glenodinium, a planktonic 

 dinof lagellate, was found in Pennel Creek and in South Sandstone 

 Creek, indicating ponding in these streams. Cyanobacteria were 

 present at all tributary sites and common to very common in upper 

 Pennel Creek, South Sandstone Creek, and upper Sandstone Creek. 



DIATOMS 



0' Fallon Creek. Most of the major diatom species from 

 0' Fallon Creek are either tolerant or very tolerant of pollution 

 (Table 6) . As a result, pollution index values for sites on 

 0' Fallon Creek indicate either minor or moderate impairment. 

 Moderate impairment by pollution is indicated at the two upstream 

 sites and minor impairment by pollution is indicated at the three 

 downstream sites. 



10 



