250 known species, more than half have been recorded from the United States. In my 

 experience, Oedogonium prefers warmer waters and slower current velocities. Oscillatoria was 

 abundant here and ranked 2"'^ in biovolume, followed by diatoms (abundant) and Mougeotia 

 (frequent). Two desmids {Cosmarium and Staurastrum) were common. This site supported a 

 total of 9 genera of non-diatom algae. 



South Fork Dearborn River at Blacktail Ranch. The sample from this station was 

 dominated by Oscillatoria (ranked 1*') and diatoms (Table 4). The only other algae in this 

 sample was an occasional desmid in the genera Closterium and Staurastrum. 



South Fork Dearborn River above FAS 434. As with the lower site on the Middle 

 Fork, this site was also dominated by Oedogonium (Table 4). Diatoms ranked 2"'' and dominated 

 the sample along with Oedogonium. Mougeotia ranked 3'^'' (common) and Ulothrix, another 

 filamentous green alga, ranked 4* and was common. An occasional cell of Tribonema was also 

 recorded in this sample. This common yellow-green alga often grows tangled among mosses 

 and vascular plants in a variety of aquatic habitats. This site supported at least 1 1 genera of non- 

 diatom algae in three divisions, including 8 genera of green algae. 



Diatoms (Table 5) 



All of the major diatom species from the Dearborn River TMDL plarjiing area are either 

 sensitive to organic pollution or only somewhat tolerant of organic pollution (Table 5). None of 

 the major diatom species are most tolerant of organic pollution, that is, none are included in 

 pollution tolerance class 1 . 



Some of the stresses indicated at some of the sites appear to be natural in origin. For 

 example, high values for the disturbance index and percent dominant species (% Achnanthidium 

 minutissimum in both cases) indicate minor stress at the two main stem sites on the Dearborn 

 River and moderate stress at the upper site on the Middle Fork of the Dearborn River (Table 5). 

 Since Achnanthidium minutissimum is an attached, pioneer species that is adapted to low nutrient 

 concentrations, these stresses are likely related to steep gradients, cold temperatures, and low 



