Mallows Bay on the Maryland side of the Potomac River in Charles County is known for a vast offshore ghost fleet widely regarded as the largest shipwreck fleet in the Western Hemisphere. Most of its wrecks are wooden steamships built for World War I by the United States Shipping Board Merchant Fleet Corporation, then sunk after the war when they became obsolete and a salvage venture failed after towing them here in 1925. Later salvage during World War II and other abandoned boats added to the site. Today the wrecks form a reef within the Mallows Bay–Potomac River National Marine Sanctuary and preserve an unusual industrial and maritime landscape.