We used agar-filled clay pots and large cages to examine how periphyton responded to in situ manipulations of nutrient availability and crayfish in a pristince Michigan stream. By day 40, nutrient additions stimulated the autotrophic portion of the periphyton community and resulted in elevated chlorophyll a, algal abundance and biovolume. Diatoms dominated the periphyton with Oscillatoria and Spirogyra the primary filamentous genera. Crayfish, (Orconectes spp.) density had no effect on any indicator of periphyton growth. Low crayfish densities ( 1 /m2) and the absence of filamentous algal dominance likely limited crayfish effects.