Effects of in-stream hiking on benthic standing stocks and drifting aquatic invertebrates and on organic matter were examined in the North Fork of the Virgin River, Zion National Park, Washington County, Utah. Densities of drifting aquatic invertebrates and organic matter increased with increasing numbers of hikers and reached a threshold level at high numbers of hikers. However, there was no apparent longer-term effect on standing stocks of benthic invertebrates or on organic matter. Densities of benthic invertebrates and organic matter did not differ among sites. Results suggest that in-stream hiking in the North Fork of the Virgin River increases drifting by invertebrates, but invertebrates from nearby undisturbed patches readily colonize impacted reaches.