It is generally expected that construction and operation of a floodplain protection project will alter a river system's hydrologic regimen, but this altered regimen also has been suspected of having major, long-term effects on the natural dynamics of riparian ecosystems that remain in gaps between large reservoirs. This study confirms that hypothesis by documenting some of those impacts in an area between Garrison Dam and Oahe Reservoir on the Missouri River in south-central North Dakota. Specifically, it examines post-dam changes in river meandering rate, floodplain forest composition, tree population structure, and tree growth rate.