Potomac River hosts a diverse range of natural features from a drowned ancient river gorge at the Fall Line above the Chain Bridge through its brackish freshwater to saltwater transition to tributary estuary where it meets Chesapeake Bay. Public works and waterfront development produced bridges, seawalls, piers, and breakwaters. A rich history of maritime commerce from Colonial times left a huge legacy of subsurface ruins, wrecks, and ballast piles...