[photo, Seagull at pier, Chesapeake Beach, Maryland]

Boating Waters

Critical Area

Main Basin


Water Frontage


Seagull at pier, Chesapeake Beach, Maryland, December 2002. Photo by Diane F. Evartt.

[photo, Skipjacks under sail] In North America, the Chesapeake Bay is the largest estuary, a semi-enclosed coastal body of water with a free connection to the open sea.

Some 35 million years ago, a bolide, an object similar to a comet or asteroid, struck the present-day Delmarva Peninsula, creating a 55-mile-wide crater. The depression created by the crater changed the course of rivers and determined the location of the Chesapeake Bay. The Bay, as we know it today, was created about 10,000 years ago when melting glaciers flooded the Susquehanna River Valley. Today, fresh water from land drainage measurably dilutes seawater within the Bay. For ocean-going ships, the Bay is navigable with two outlets to the Atlantic Ocean: north through the Chesapeake and Delaware Canal in Cecil County, and south through the mouth of the Bay between the Virginia capes.

Native Americans living along its shores gave the Bay an Algonquian name. Chesepiook, meaning "great shell-fish bay," was used to signify the abundance of Bay crabs, oysters, and clams. In June 1608, Captain John Smith led two voyages throughout the Chesapeake Bay, and in its midst European settlers first landed at St. Clement's Island, Maryland, in 1634. Through the lower portion of the Bay, pirates settled and attacked ships off the coast. And, at its southernmost reaches during the Civil War, the first ironclads, the Confederate Virginia (formerly the USS Merrimack) and the Union's Monitor, fought to a draw near Hampton Roads, Virginia, in March 1862. Many shipwrecks, remains of vessels sunk by natural forces, human error, or attack, lie deep under the Chesapeake Bay.

Skipjacks under sail. Photo by Chuck Prahl.

Generations of watermen have made their living harvesting the bounty of the Bay, while recreational fishing, hunting, and boating attract millions of people each year and contribute significantly to Maryland's economy. Major annual seafood harvests include millions of bushels of crabs, oysters, clams, and eels.

Three Maryland agencies bear particular responsibility for Bay matters. The Department of Agriculture directs the Office of Resource Conservation which oversees Chesapeake Bay Agricultural Programs. The Department of the Environment works on behalf of the Bay through its Science Services Administration. The Department of Natural Resources supports the work of the Critical Area Commission for the Chesapeake and Atlantic Coastal Bays (formerly Chesapeake Bay Critical Area Commission) and oversees Aquatic Resources.

Information about the Bay, including its history and effect on regional culture, may be found at the Chesapeake Bay Maritime Museum at St. Michaels.



Maryland 1,726 square miles
Virginia 1,511 square miles


195 miles


(widest near Cape Charles, Virginia) 30 miles
(narrowest at Annapolis) 4 miles


4,600 miles


average 25 feet
greatest (southeast of Annapolis) 174 feet


at Annapolis 1 foot
at head 2 feet
at mouth 3 feet


18 trillion gallons

(parts per thousand)

at mouth 30 ppt
midway to head 15 ppt
above fall line 00 ppt
surface to bottom 2-3 ppt


Sixteen of Maryland's 23 counties and Baltimore City border on tidal water.


The rivers, creeks, and streams which flow into the Bay, the land surrounding them, and the Bay itself make up the Chesapeake Bay watershed. Three main tributaries flow into the Bay, and contribute 80% of the Bay's fresh water. The largest of these is the Susquehanna River, followed by the Potomac River, and Virginia's James River. The total number of tributaries to the Bay watershed is 419, and the watershed area itself totals some 64,000 square miles in parts of six states: Maryland, Delaware, Pennsylvania, New York, Virginia, West Virginia-and the District of Columbia.

The Bay watershed provides rich habitat for an abundance of life. In addition to resident species of fish and wildlife, the Bay supports large winter populations of migratory waterfowl and provides spawning, nursery and feeding grounds for ocean fish. This diversity enables some 2,700 different species of plants and animals to live in the Bay area. Research on the Chesapeake Bay and its watershed is conducted by the University of Maryland Center for Environmental Science.

According to the Chesapeake Bay Program, the number of people living within the Bay's watershed was 17.9 million in 2014, up from 17.8 million in 2013. Scientists project that the population of the watershed will approach 21.4 million by 2040.

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