The North Fork of the Virgin River is a flash flood-prone southwest desert river and a popular adventure trek in Zion National Park for thousands of people each year.  While flash floods cause unpredictable, high-intensity disturbance, hikers cause constant and predictable low-intensity disturbance.  We sought to evaluate the impacts of in-stream hiking on periphyton and aquatic invertebrates in the context of natural disturbance regimes.  From May through August 2006, ca. 163,000 visitors (an average of 1,988 per day) hiked the river in our study reach.  Periphyton was collected in hiking paths and multiple drift net samples were collected downstream of hiker paths in reaches of high, moderate, and low hiker densities each month during this visitor use period.  There was a 93% reduction in chlorophyll a at the high-impact site compared to the low-impact site.  Overall, aquatic invertebrate drift density was positively associated with the number of hikers traveling upstream of the drift nets.  These results suggest that anthropogenic disturbance is nearly constant during the visitor use season, creating a disturbance regime fundamentally different than the more infrequent and high-intensity disturbance created by flash floods.