The largest and most well known geographic feature of Maryland is the Chesapeake Bay, the worlds largest estuary. At one time it was called the worlds protein basket because it produced so much seafood in the form of fish and shellfish, in particular its most famous product Blue Crabs. Today the Chesapeake Bay is a poster child for what happens from overfishing and pollution, but Maryland leads the country in many progressive "Save the Bay" programs to save wetlands, halt the flow of nitrogens and pollutents from the over 12 million people who live in its watershed from Pennsylvania to Virginia. The Chesapeake Bay is a magnet for sailing and fishing sports activities.
The state is bounded to the south by the Potomac River, which offers opportunities for boating, and bicycling along the Chesapeake and Ohio Canal Trail, leading from Washington, D.C. to Cumberland. The western part of the state is much more mountainous than the eastern lowlands, and offers hiking along the Appalachian Trail, whitewater recreation in the Youghiogheny River, and historical sites such as Antietam Battlefield, where one of the bloodiest battles of the American Civil War was fought.