The Chesapeake Bay is the largest estuary (186 mi [300 km] long) in the United States. The Bay was formed 1500 years ago by the retreat of glaciers and the subsequent sea level rise that inundated the lower Susquehanna River valley. The Bay has a drainage basin of 64,076 square miles (166,000 sq km) covering six states and running through Pennsylvania, Maryland, the District of Columbia, and Virginia before entering the Atlantic Ocean. While 150 rivers enter the Bay, a mere eight account for 90% of the freshwater input, with the Susquehanna alone contributing nearly half. Chesapeake Bay is a complex system, composed of numerous habitats and environmental gradients.

Chesapeake Bay's abundant natural resources attracted native Americans, first settling on its shores. The first European record of the Bay was in 1572 and the area surrounding Chesapeake Bay was rapidly colonized by Europeans. In many ways, the United States grew up around Chesapeake Bay...