Dendron Swamp Natural Area Preserve is a 636-acre protected area along the Blackwater River in Sussex County, Virginia, known for its unusually old and well-preserved bald cypress and tupelo swamp. Along about two miles of river corridor, canopy trees rise more than 98 feet, and the forest shows only occasional signs of logging. Some of the largest bald cypresses are believed to be more than 600 years old. The preserve also provides important wildlife habitat, including a nesting site for great blue herons. Within it, the 19-acre Charles C. Steirly Natural Area is an essentially virgin old-growth swamp recognized as a National Natural Landmark in 1974.