Introduction 



This report describes the non-diatom algae in 299 periphyton 

 and phytoplankton samples taken at 49 stations in the Yellowstone 

 River and tributaries between April 1973 and November 1975. (Station 

 descriptions and the number of samples analyzed per station are 

 provided in appendices A and B.) The ecological requirements of, 

 and the implications of altered flow regimes on, the Yellowstone's 

 dominant non-diatom taxon-- C1adophora qlomerata- -are discussed at 

 length. Prior and ongoing Yellowstone River algae research efforts, 

 which in many cases complement the results reported here, are reviewed. 

 A key to the common algae of the Yellowstone River is provided (Appendix 

 D ). 



Other than C. glomerata and three other species, one of which is 

 unispecific and the other two with distinct and easily recognizable 

 characteristics, only generic indentifications are provided. Although 

 a generic approach forfeits a certain amount of species-related eco- 

 logical information, it allowed for a much more rapid analysis of the 

 samples in the face of the apporaching expiration of the Yellowstone 

 water moratorium. Moreover, suitable algal material and keys for 

 identifying many species were not available to the author. 



In August and September 1952 the Public Health Service (9) sur- 

 veyed the phytoplankton in the Yellowstone, CI arks Fork, Bighorn 

 and Powder rivers at 11 stations between Laurel and 61 endive in re- 

 sponse to complaints of taste and odor problems in domestic water 

 supplies. About 10 years later, Williams (16), also with the Public 



-4- 



