Yellow-bellied slider (Trachemys scripta scripta), in the Washington Ditch in the Great Dismal Swamp National Wildlife Refuge. Suffolk, Virginia. Please click photo for full view. 

The ditch is actually a shallow canal, about 18 feet wide (5.5 m). It was constructed in 1763 as part of a logging scheme devised by George Washington, who surveyed and oversaw the digging, which was done by slaves rented from local plantations. The canal system was designed to provide drainage and access, and a means for floating lumber out of the swamp – primarily cypress for shipbuilding, and cedar for housing. The network of ditches later provided access for slaves who fled into the swamp  seeking freedom – a dangerous and uncomfortable early stop on the Underground Railroad before reaching water routes to the north through Portsmouth and Norfolk.