The South Carolina national park that protects old-growth bottomland hardwood forest is Congaree National Park.
Located southeast of Columbia, Congaree preserves a floodplain shaped by periodic overflows of the Congaree River and nearby Cedar Creek. Its forest includes bald cypress, water tupelo, loblolly pine, sweetgum, and several species of oak. The park is known for exceptionally tall trees and one of the highest temperate deciduous forest canopies in the world.
The area became a national park on November 10, 2003, after decades of conservation campaigning. It was previously protected as Congaree Swamp National Monument, established in 1976. Despite its nickname, much of Congaree is not a permanently flooded swamp; it is bottomland forest that floods at intervals.
The answer is sometimes confused with other wetland parks, especially Biscayne, which is primarily a marine park in Florida. Visitors commonly experience Congaree via the elevated Boardwalk Loop, while canoe and kayak routes reveal more of its floodplain ecology.