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The Chesapeake Bay ( ) is the largest estuary in the United Statesmarker. It lies off the Atlantic Oceanmarker, surrounded by Marylandmarker and Virginiamarker. The Chesapeake Bay's watershed covers in the District of Columbiamarker and parts of six states: New Yorkmarker, Pennsylvaniamarker, Delawaremarker, Marylandmarker, Virginiamarker, and West Virginiamarker. 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'smarker Plum Point (near Newtown) and the Harford Countymarker 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 . Depth of the bay is and maximum depth of bay is .

The bay is spanned in two places. The Chesapeake Bay Bridgemarker crosses the bay in Maryland from Sandy Point (near Annapolismarker) to Kent Islandmarker; the Chesapeake Bay Bridge-Tunnel in Virginia connects Virginia Beachmarker to Cape Charlesmarker.

The word Chesepiooc is an Algonquian word referring to a village "at a big river." It is the seventh oldest surviving English place-name in the U.S., first applied as "Chesepiook" by explorers heading north from the Roanoke Colony into a Chesapeake tributary in 1585 or 1586. In 2005, Algonquian linguist Blair Rudes "helped to dispel one of the area's most widely held beliefs: that 'Chesapeake' means something like 'Great Shellfish Bay.' It doesn't, Rudes said. The name might actually mean something like 'Great Water,' or it might have been just a village at the bay's mouth." In contrast with many similar bodies of water, such as Delaware Baymarker or San Francisco Baymarker, the Chesapeake Bay is almost always preceded by the article the in usage.


The Chesapeake Bay is the ria, or drowned valley, of the Susquehanna, meaning that it was where the river flowed when the sea level was lower. It is not a fjord, as the Laurentide Ice Sheet never reached as far south as the northernmost point on the bay.

The Bay's geology, its present form, and its very location were created by a bolide impact event at the end of the Eocene (about 35.5 million years ago), forming the Chesapeake Bay impact cratermarker and the Susquehanna river valley much later. The Bay itself was formed starting about 10,000 years ago when rising sea levels at the end of the last ice age flooded the Susquehanna river valley. Parts of the bay, especially the Calvert County, Marylandmarker coastline, are lined by cliffs composed of deposits from receding waters millions of years ago. These cliffs, generally known as Calvert Cliffsmarker, are famous for their fossils, especially fossilized shark teeth, which are commonly found washed up on the beaches next to the cliffs. Scientists' Cliffs is a beach community in Calvert Countymarker named for the desire to create a retreat for scientists when the community was founded in 1935.

Much of the bay is quite shallow. At the point where the Susquehanna River flows into the bay, the average depth is , although this soon diminishes to an average of from the city of Havre de Gracemarker for about , to just north of Annapolis. On average, the depth of the bay is 21 feet (7 meters), including tributaries; over 24% of the bay is less than deep.

The climate of the area surrounding the bay is primarily humid subtropical, with hot, very humid summers and cold to mild winters. Only the area around the mouth of the Susquehanna River is continental in nature, and the mouth of the Susquehanna River and the Susquehanna flats often freeze in winter. It is exceedingly rare for the surface of the bay to freeze in winter, as happened most recently in the winter of 1976-1977.

Since the bay is an estuary, it has fresh water and brackish water. Brackish water has three salinity zones — oligohaline, mesohaline, and polyhaline. The fresh water zone runs from the mouth of the Susquehanna River to north Baltimoremarker. The oligohaline zone has very little salt. Salinity varies from 0.5 ppt to 10 ppt and freshwater species can survive there. The north end of the oligohaline zone is north Baltimore and the south end is the Chesapeake Bay Bridge. The mesohaline zone has a medium amount of salt and runs from the Bay Bridge to the mouth of the Rapahannock River. Salinity there ranges from 10.7 ppt to 18 ppt. The polyhaline zone is the saltiest zone and some of the water can be as salty as sea water. It runs from the mouth of the Rappahannock Rivermarker to the mouth of the bay. The salinity ranges from 18.7 ppt to 36 ppt. (36 ppt is as salty as the ocean.)


Spanish explorer Lucas Vásquez de Ayllón sent an expedition out from Hispaniolamarker in 1525, led by Captain Pedro de Quejo, which reached the mouth of the Chesapeake and Delaware Baysmarker and may have been the first European expedition to explore parts of the Chesapeake Bay. De Ayllón established a short-lived Spanishmarker mission settlement, "San Miguel de Gualdape", in 1526 along the Atlanticmarker coast. Many scholars doubt the assertion that it was as far north as the Chesapeake; most place it in present-day Georgiamarker's Sapelo Islandmarker.

Captain John Smith of Englandmarker explored and mapped the bay between 1607 and 1609. The "Captain John Smith Chesapeake National Historic Trailmarker", the United States' first-ever all-water National Historic Trail, was created in July 2006. The bill passed by voice vote in the House of Representatives and by unanimous consent in the Senate.

The Chesapeake Bay was the site of the Battle of the Chesapeake in 1781, during which the Frenchmarker fleet defeated the Royal Navy in the decisive naval battle of the American Revolutionary War.

Today, the Calvert Cliffs Nuclear Power Plantmarker uses water from the bay to cool its reactor.

The bay is also known for the Chesapeake Bay Retriever, a dog breed developed in this area.


The largest rivers flowing directly into the bay, from north to south, are:

Fishing industry

A charter fishing boat on the Chesapeake Bay
The bay was once known for its great seafood production, especially blue crabs, clams and oysters. The plentiful oyster harvests led to the development of the skipjack, the state boat of Maryland, which is the only remaining working boat type in the United Statesmarker still under sail power. Other characteristic bay area workboats include:

Today, the body of water is less productive than it used to be, because of runoff from urban areas (mostly on the Western Shore) and farms (especially on the Eastern Shore), over harvesting, and invasion of foreign species. The bay still yields more fish and shellfish (about 45,000 short tons or 40,000 tonnes yearly) than any other estuary in the United States.

The bay is famous for its rockfish, also known as striped bass. Once on the verge of extinction, rockfish have made a significant comeback due to legislative action that put a moratorium on rockfishing, which allowed the species to repopulate. Rockfish are now able to be fished in strictly controlled and limited quantities.

Oyster farming is a growing industry for the bay to help maintain the bay's productivity as well as a natural effort for filtering impurities in the bay in an effort to reduce the disastrous effects of man-made pollution.

In 2005, local governments began debate on the introduction to certain parts of the bay of a species of Asian oyster, to revive the lagging shellfish industry.

Deteriorating environmental conditions

In the 1970s, the Chesapeake Bay was discovered to contain one of the planet's first identified marine dead zones, where hypoxic waters were so depleted of oxygen they were unable to support life, resulting in massive fish kills. Today the bay's dead zones are estimated to kill 75,000 tons of bottom-dwelling clams and worms each year, weakening the base of the estuary's food chain and robbing the blue crab in particular of a primary food source. Crabs themselves are sometimes observed to amass on shore to escape pockets of oxygen-poor water, a behavior known as a "crab jubilee". Hypoxia results in part from large algal blooms, which are nourished by the runoff of farm and industrial waste throughout the watershed. This algae prevents sunlight from reaching the bottom of the bay while alive and deoxygenates the bay's water when it dies and rots. The erosion and runoff of sediment into the bay, exacerbated by devegetation, construction and the prevalence of pavement in urban and suburban areas, also blocks vital sunlight. The resulting loss of aquatic vegetation has depleted the habitat for much of the bay's animal life. Beds of eelgrass, the dominant variety in the southern bay, have shrunk by more than half there since the early 1970s. Overharvesting, pollution, sedimentation and disease has turned much of the bay's bottom into a muddy wasteland.

One particularly harmful algae is Pfiesteria piscicida, which can affect both fish and humans.

Depletion of oysters

While the bay's salinity is ideal for oysters, and the oyster fishery was at one time the bay's most commercially viable, the population has in the last fifty years been devastated. Maryland once had roughly 200,000 acres of oyster reefs. Today it has about 36,000. It has been estimated that in pre-colonial times, oysters could filter the entirety of the Bay in about 3.3 days; by 1988 this time had increased to 325 days. The harvest's gross value decreased 88% from 1982 to 2007.

The primary problem is overharvesting. Lax government regulations allow anyone with a license to remove oysters from state-owned beds, and although limits are set they are not strongly enforced. The overharvesting of oysters has made it difficult for them to reproduce, which requires close proximity to one another. A second cause for the oyster depletion is that the drastic increase in human population caused a sharp increase in pollution flowing into the bay.

The bay's oyster industry has also suffered from two diseases: MSX and Dermo.

Oyster recovery attempts

The depletion of oysters due to overharvesting and damaged habitat has had a particularly harmful effect on the quality of the bay. Oysters serve as natural water filters, and their decline has further reduced the water quality of the bay. Water that was once clear for meters is now so turbid that a wader may lose sight of his feet before his knees are wet.

Efforts of federal, state and local governments, working in partnership through the Chesapeake Bay Program, and the Chesapeake Bay Foundation and other nonprofit environmental groups, to restore or at least maintain the current water quality have had mixed results. One particular obstacle to cleaning up the bay is that much of the polluting substances arise far upstream in tributaries lying within states far removed from the bay itself. Despite the state of Maryland spending over $100 million to restore the bay, conditions have continued to grow worse. Twenty years ago, the bay supported over six thousand oystermen. There are now fewer than 500.

Efforts to repopulate the bay with via hatcheries have been carried out by a group called the Oyster Recovery Partnership, with some success. They recently placed 6 million oysters on eight acres of the Trent Hall sanctuary. Scientists from the Virginia Institute of Marine Sciencemarker at the College of William & Marymarker claim that experimental reefs created in 2004 now house 180 million native oysters, Crassostrea virginica, which is far less than the billions that once existed.


The Chesapeake Bay is a main feature for tourists who visit Maryland and Virginia each year. Fishing, crabbing, swimming, boating and sailing are extremely popular activities enjoyed on the waters of the Chesapeake Bay. As a result, tourism has a notable impact on Maryland's economy.

See also


  1. Also shown as "Chisupioc" (by John Smith) and "Chisapeack", in Algonquian "Che" means "big" or "great", "sepi" means river, and the "oc" or "ok" ending indicated something (a village, in this case) "at" that feature. "Sepi" is also found in another placename of Algonquian origin, Mississippi. The name was soon transfered by the English from the big river at that site to the big bay.
  2. Other sources give values of 25 feet (e.g. ) or 30 feet deep ( )
  3. Oysters: Gem of the Ocean, The Economist, December 8, 2008; accessed September 2, 2009.
  4. Program turns pork into oysters, Jesse Yeatman, South Maryland Newspapers Online, August 12, 2009.
  5. Oysters Are on the Rebound in the Chesapeake Bay, Henry Fountain, The New York Times, August 3, 2009; accessed September 8, 2009.

Further reading

  • Cleaves, E.T. et al. (2006). Quaternary geologic map of the Chesapeake Bay 4º x 6º quadrangle, United States [Miscellaneous Investigations Series; Map I-1420 (NJ-18)]. Reston, VA: U.S. Department of the Interior, U.S. Geological Survey.
  • Phillips, S.W., ed. (2007). Synthesis of U.S. Geological Survey science for the Chesapeake Bay ecosystem and implications for environmental management [U.S. Geological Survey Circular 1316]. Reston, VA: U.S. Department of the Interior, U.S. Geological Survey.

Bay Area Publications

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