Short-term caging experiments were conducted to examine the direct effects that the crayfishOrconectes propinquushas on benthic communities. Stream-colonized tiles (precolonized within the stream) and uncolonized clay tiles were placed in eight elevated, hardware-cloth metal cages. Four cages had crayfish (~8 crayfish m−2); the other four were empty controls. Chlameasured on pre-colonized tiles five days after the commencement of the experiment indicated that crayfish had no significant effect on algal biomass.O. propinquusalso had no measurable impact on snail abundance from tiles sampled after five days. Samples taken after seventeen days from initially uncolonized tiles showed that crayfish had a direct negative effect on diatom abundance. Tiles with crayfish had 50% fewer diatoms than control cages, although there were no differences in the relative abundance of the 6 most abundant diatom genera. Insects collected from these tiles (day 17) did not differ in density, relative abundance (by order), or size between crayfish treatments. The results indicate that crayfish can have direct negative effects on the diatom portion of the algal community.