Salmon carcasses from spawning migrations can be retained in stream ecosystems behind woody debris, boulders, and other substrata where they contribute nutrients and organic matter to the stream biota. We hypothesized that carcasses would enhance algal and microbial growth and wood decomposition. To test this, we placed wood and clay pot substrata directly downstream of decomposing salmon in the Little Knife River, Minn., U.S.A., and compared total biofilm biomass on substrata in the vicinity of decomposing salmon and upstream of salmon carcasses. After 335 days in the stream, there was a significant mass loss of wood but no apparent effect of carcass decomposition on wood mass loss. Significantly, more chlorophyll a was found on both wood and pots when carcasses were present (p < 0.05) compared with controls. Stable isotope analyses suggest that the fish-derived nitrogen was taken up by the periphyton and total biofilm. Biofilm on the pots and wood near fish showed a significant increase in ash-free dry mass (p < 0.05). We conclude that fish-derived nutrients enhanced algal and total biofilm growth but did not significantly influence wood decomposition.