Congaree National Park in South Carolina is defined by the Congaree River floodplain, which covers about 80 percent of the park. The river’s meandering course creates a landscape of old‑growth bottomland hardwood forest, oxbow lakes, and sloughs that support diverse wildlife.

The park contains one of the largest remaining tracts of old‑growth bottomland hardwood forest in the United States. The floodplain formed as the Congaree River shifted across flat terrain, carving bends, point bars, and abandoned channels over time.

Water moves faster on the outer banks of bends, causing erosion, while slower flow on the inner banks deposits sediment and builds point bars. When a bend is cut off from the main channel, it forms a U‑shaped oxbow lake. Weston Lake, 1.2 miles from the visitor center, remains deep and lacks the shallow sediment layer found in many other oxbow lakes. Bates Old River, a roughly 4‑mile abandoned channel, is one of the longest oxbow lakes in South Carolina. Low‑lying water‑filled features such as sloughs host cypress‑tupelo forests adapted to frequent flooding.

Logging attempts in the 1880s were limited by flooding, muddy roads, and mosquito conditions, allowing most of the floodplain forest to remain intact. Congress designated the area a national monument in 1976, and it became a national park in 2003. The river overflows its banks several times per year, typically in winter and early spring, and after hurricanes or heavy rains. These floods deposit nutrient‑rich silt that sustains the forest and contributes to the high number of large trees recorded in the park.

Species such as possumhaw, water hickory, loblolly pine, laurel oak, swamp tupelo, and sweetgum have held size records at various times. Ongoing monitoring continues to track tree sizes and floodplain dynamics, with the potential for climate variability to alter flood frequency and ecosystem composition.

The park remains a focus for ecological research and public recreation, with future studies expected to clarify how changing precipitation patterns may affect the floodplain.