Short-term impacts of commercial barge traffic on fish eggs, larvae, young-of-the-year (age-0) fishes, and small adults in the main channel of the upper Mississippi River were examined. Barge passages caused significant changes in the distribution of eggs and larvae in the study area. The mean catch of ichthyoplankton was reduced in both surface and bottom waters for 90 min after passage of vessels (generally loaded barges) downstream. The effects of upstream traffic (unloaded barges) on catch ranged from nil in surface or bottom samples to short-term increases in surface samples immediately after passage. No consistent effect on the catch of age-0 or small adult fishes in surface or bottom trawls was evident. Physical damage to eggs, but not to larvae or small fish, was significant.