The diatom flora was studied at four stations on Fall Creek upstream from its confluence with White River at Tenth Street, Indianapolis, Indiana, over a three month period, December through February 1961-2. The entire course of the Creek studied was classified as fairly clean water. Pollution was due largely to contamination by sanitary wastes. The water had an average temperature of 2.5ºC and an average of slightly alkaline reaction. The communities were composed of a few species well represented and many species sparsely represented.