The Savannah River was impounded in the 1950s near Augusta, Georgia (USA) by Thurmond Dam, a large hydroelectric facility. The objectives of this study were twofold: (1) Identify flooding patterns in areas of the Savannah River floodplain containing Taxodium distichum (L.) Rich, and how these patterns have been affected by dam operations; (2) Identify diameter growth responses of Taxodium to flooding patterns, and whether growth has changed in response to dam-induced hydrologic changes. River gage records revealed that higher elevation sites were significantly drier in the post-dam era. These sites also showed a significant post-dam increase in basal area increment growth. Low-elevation sites did not show significant hydrologic or growth differences between pre- and post-dam eras, but did show decreased sensitivity of growth to flooding in the post-dam era. This study is the first to quantitatively demonstrate an effect of Thurmond Dam on the hydrologic conditions and growth patterns of floodplain trees.