Mallows Bay–Potomac River National Marine Sanctuary is an 18-square-mile protected stretch of the Potomac River in Maryland that combines a rich archaeological record with a living tidal habitat. Designated in 2019, it includes more than 200 shipwrecks, most famously the Ghost Fleet of 118 wooden steamships built for World War I but never used in combat, then salvaged, burned, and scuttled in Mallows Bay. The sanctuary also preserves sites linked to Native American history, especially the Piscataway and Patawomeck peoples, as well as African-American history from the 17th century onward. Its wrecks now help support birds, plants, and shoreline habitat, making the area a meeting place of maritime, cultural, and environmental history.