What Is a Watershed?

A watershed—sometimes called a basin or drainage basin—is an area of land that drains into a particular river, lake or other body of water. Some watersheds, like that of a stream or creek, are small. Others, like the Chesapeake Bay watershed, are large.

An elevation map of the Chesapeake Bay watershed, from the middle of New York to the north through much of Virginia to the south. The map also includes parts of West Virginia, Pennsylvania, Maryland, and Delaware, as well as Washington DC. The cities of Richmond, Virginia; Annapolis, Maryland; and Harrisburg, Pennsylvania are marked. State boundaries are marked with dotted white lines.

What is the Chesapeake Bay watershed?

The Chesapeake Bay watershed spans more than 64,000 square miles, encompassing parts of six states—Delaware, Maryland, New York, Pennsylvania, Virginia and West Virginia—and the entire District of Columbia.

More than 18 and a half million people and over 36,000 species of plants and animals live in the Chesapeake Bay watershed. The land-to-water ratio of the watershed is 14:1—the largest of any coastal water body in the world. This means that what we do on the land has a big impact on the health of the Bay.

What rivers flow through the Bay watershed?

The Susquehanna, Potomac, Rappahannock, York and James rivers are the five largest rivers in the Chesapeake Bay watershed.

More than 100,000 streams, creeks and rivers—called tributaries—thread through this watershed. Each watershed resident lives within a few miles of at least one tributary, which acts like a pipeline that connect our communities to the Bay.

Each of the streams, creeks and rivers in the Bay watershed has its own watershed, called sub-watersheds, small watersheds or local watersheds.

Protecting the watershed

In a watershed, pollution that occurs upstream carries downstream, eventually impacting the health of the Chesapeake Bay. To protect the estuary, we need to reduce pollution and protect land across the entire watershed, including each of the more than 100,000 streams. State and local leaders, environmental organizations and community groups from across the region collaborate through the Chesapeake Bay Program to make this happen.

Just as a watershed connects residents living upstream and downstream, the work of the Chesapeake Bay Program involves many cross-benefits and requires the collaboration of many stakeholders. Kristin Saunders, the Chesapeake Bay Program's Cross Program Coordinator, describes the interconnected work of the partnership's efforts to restore the Chesapeake Bay watershed. (Video produced by Will Parson/Chesapeake Bay Program)