The Chesapeake Bay ( /ˈtʃɛsəpiːk/ CHESS-ə-peek) is the largest estuary in the United States. It lies off the Atlantic Ocean, surrounded by Maryland and Virginia. The Chesapeake Bay's drainage basin covers 64,299 square miles (166,534 km²) in the District of Columbia and parts of six states: New York, Pennsylvania, Delaware, Maryland, Virginia, and West Virginia. More than 150 rivers and streams drain into the bay.

The Chesapeake Bay is approximately 200 miles (300 km) long, from the Susquehanna River in the north to the Atlantic Ocean in the south. At its narrowest point between Kent County's Plum Point (near Newtown) and the Harford County shore near Romney Creek, the bay is 2.8 miles (4.5 km) wide; at its widest point, just south of the mouth of the Potomac River, it is 30 miles (50 km) wide. Total shoreline for the bay and its tributaries is 11,684 miles (18,804 km), and the surface area of the bay and its major tributaries is 4,479 square miles (11,601 km²). Average depth of the bay is 46 feet (14 m) and the maximum depth is 208 feet (63 m).