observed at S-3. Green algae accounted for most of these genera. 

 The average number of non-diatom genera observed in least 

 impaired plains streams was 13 (range 9-19) (Bahls 1993). 



The most abundant non-diatom algae at' S-2 were Chaetophora 



I 



and Zygnema (Table 5) . Chaetophora prefers cold, running waters. 

 Microspora, which ranked second in biovolume to diatoms at S-3, 

 also prefers cool water, but is more often found in slack water 

 habitats, like pools and ditches (Smith 1950). 



Competition with aquatic mosses at S-3 may help to explain 

 the smaller number of algal genera observed here. Aquatic mosses 

 are perennial plants that indicate a constant supply of cool 

 water, which is consistent with the nature of a spring creek. 

 Since Spring Creek closely parallels the Teton River for much of 

 its length (Map 1) , it likely receives much of its flow from this 

 parent stream. Spring Creek also receives water from Eureka 

 Reservoir via seepage from an irrigation canal that runs parallel 

 to and upslope from the creek (Darrin Kron, MDEQ, personal 

 communication, February 6, 2001). 



DIATOMS 



All but one of the seven major diatom species in Spring 

 Creek were sensitive to organic pollution (Table 6) . Dominance 

 by sensitive diatoms is reflected in the relatively high 

 pollution index values at both stations. These are particularly 

 high for prairie streams and indicate little organic loading. 



A unique feature of the Spring Creek diatom assemblage is 

 dominance by species of Fragilaria. Diatoms in this genus are 

 usually unattached and tychoplanktonic, indicating relatively low 

 turbulence and slow current velocities. 



