Health Service, determined the percent occurrence of plankton algae 

 at Sidney over a one year period. More recently, Stadnyk (12) measured 

 biomass standing crop and autotrophic index of the periphyton (attached) 

 community at three stations between Gardiner and Billings. Westinghouse 

 (14) identified and counted plankton (suspended) algae at two stations 

 near the mouth of Armells Creek. Bahls (1) (also reported in Montana 

 Department of Natural Resources and Conservation (6)) identified 

 suspended algae collected in three net samples taken near the mouth 

 of the Bighorn River. An up-to-date review of Yellowstone algae work 

 was presented to the Fort Union Coal Field Symposium in April 1975 (2). 

 Since October 1974, the Geological Survey (5) has been sampling monthly 

 for phytoplankton and quarterly for periphyton and chlorophyll at a 

 total of five stations on the Yellowstone, Tongue, Powder and Bighorn 

 rivers. An intensive study of the microflora of the middle river be- 

 tween Laurel and Huntley, and its response to a variety of waste dis- 

 charges, was prepared for presentation at the 1976 annual meeting of 

 the Montana Academy of Sciences (3). 



The 1952 Public Health Service survey (9) provides opportunity 

 for historical comparison with more recent findings. That survey and 

 the studies by Williams (16) and the Geological Survey (5), all of 

 which apparently sampled for nannoplankton, allow for comparison with 

 the net plankton described in the present study. Additional taxa 

 identitied in these three studies and not in the present study are 

 included in the checklist in Appendix C. 



