The lower segments of tributary streams provide the only remaining backwater habitat for much of the lower Missouri River. We describe the movements of adult channel catfishIctalurus punctatusbetween a 13-km segment of the Missouri River and a tributary, Perche Creek, that enters the river in this segment to determine the extent to which river-dwelling fish use the tributary habitats. We used mark-recapture techniques to describe movements offish larger than 250 mm in total length between these habitats during a 22-month period. Most fish (59%) initially caught, recaptured, or both in the Missouri River moved into or out of Perche Creek, and most of these transient fish (72%) used the lower 8 km of the tributary. The tributary population was made up predominantly of resident fish (79%), which were initially caught and recaptured in Perche Creek. Channel catfish moved greater distances in the spring than in the fall and were more likely to move upstream in the spring and downstream in the fall. Fish shorter than 250 mm were more abundant in the river than in the creek and made up 45 and 35% of the catches in each area, respectively. Furthermore, of the fish longer than 280 mm, a greater proportion of the fish resident in the river (44%) than in the creek (33%) were longer than 380 mm. More fish longer than 380 mm moved from the creek to the river (44%) than from the river to the creek (26%). Thus, the tributary habitat was used most frequently by fish 280–380 mm long. Flathead catfishPylodictis olivariswere much less abundant in the creek than in the river and did not provide sufficient sample sizes to evaluate movement patterns. However, based on abundances in our catches, the proportion of river flathead catfish using the creek was much lower than for channel catfish. Most of the few flathead catfish found in the creek were longer than 280 mm.