The Chesapeake Bay (/ˈtʃɛsəpiːk/ CHESS-ə-peek) is an estuary in the U.S. states of Maryland and Virginia. The Bay is located in the Mid-Atlantic region and is primarily separated from the Atlantic Ocean by the Delmarva Peninsula with its mouth located between Cape Henry and Cape Charles.^[2] With its northern portion in Maryland and the southern part in Virginia, the Chesapeake Bay is a very important feature for the ecology and economy of those two states, as well as others. More than 150 major rivers and streams flow into the Bay's 64,299-square-mile (166,534 km2) drainage basin, which covers parts of six states (New York, Pennsylvania, Delaware, Maryland, Virginia and West Virginia) and all of Washington, D.C.^[2][3]

The Bay is approximately 200 miles (320 km) long from its northern headwaters in the Susquehanna River to its outlet in the Atlantic Ocean. It is 2.8 miles (4.5 km) wide at its narrowest (between Kent County's Plum Point near Newtown and the Harford County shore near Romney Creek) and 30 miles (48 km) at its widest (just south of the mouth of the Potomac River). Total shoreline including tributaries is 11,684 miles (18,804 km), circumnavigating a surface area of 4,479 square miles (11,601 km2). Average depth is 21 feet (6.4 m), reaching a maximum of 174 feet (53 m).^[4] The Bay is spanned twice, in Maryland by the Chesapeake Bay Bridge from Sandy Point (near Annapolis) to Kent Island and in Virginia by the Chesapeake Bay Bridge-Tunnel connecting Virginia Beach to Cape Charles. Known for both its beauty and bounty, the Bay has become "emptier", with fewer crabs, oysters and watermen in past years.^[5] Recent restoration efforts begun in the 1990s have been ongoing and show potential for growth of the native oyster population.^[6][7] The health of the Chesapeake Bay improved in 2015, marking three years of gains over the past four years, according to a new report by the University of Maryland.^[8]

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 United States, first applied as "Chesepiook" by explorers heading north from the Roanoke Colony into a Chesapeake tributary in 1585 or 1586. The name may also refer to the Chesapeake people or the Chesepian, a Native American tribe who inhabited the area now known as South Hampton Roads in the U.S. state of Virginia. They occupied an area that is now the Norfolk, Portsmouth, Chesapeake, and Virginia Beach areas.^[9] 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 does not, Rudes said. The name might actually have meant something like 'great water,' or it might have just referred to a village location at the Bay's mouth."^[10] In addition, the name is almost always prefixed by "the" in usage by local residents: "The Chesapeake", "The Chesapeake Bay" and "The Bay".^[11]

The Chesapeake Bay is an estuary to the North Atlantic, lying between the Delmarva Peninsula to the east and the North American mainland to the west. It is the ria, or drowned valley, of the Susquehanna River, meaning that it was the alluvial plain where the river flowed when the sea level was lower. It is not a fjord, because the Laurentide Ice Sheet never reached as far south as the northernmost point on the Bay. North of Baltimore, the western shore borders the hilly Piedmont region of Maryland; south of the city the Bay lies within the state's low-lying coastal plain, with sedimentary cliffs to the west, and flat islands, winding creeks and marshes to the east. The large rivers entering the Bay from the west have broad mouths and are extensions of the main ria for miles up the course of each river.

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 crater and the Susquehanna River valley much later. The Bay 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.^[3] Parts of the Bay, especially the Calvert County, Maryland, coastline, are lined by cliffs composed of deposits from receding waters millions of years ago. These cliffs, generally known as Calvert Cliffs, 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 County named for the desire to create a retreat for scientists when the community was founded in 1935.^[12]

Much of the Bay is shallow. At the point where the Susquehanna River flows into the Bay, the average depth is 30 feet (9 m), although this soon diminishes to an average of 10 feet (3 m) southeast of the city of Havre de Grace, Maryland, to about 35 feet (11 m) just north of Annapolis. On average, the depth of the Bay is 21 feet (6.4 m), including tributaries;^[13] over 24 percent of the Bay is less than 6 ft (2 m) deep.^[14]

Because the Bay is an estuary, it has fresh water, salt water and brackish water. Brackish water has three salinity zones: oligohaline, mesohaline, and polyhaline. The freshwater zone runs from the mouth of the Susquehanna River to north Baltimore. The oligohaline zone has very little salt. Salinity varies from 0.5 ppt (parts per thousand) 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 Rappahannock 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 River to the mouth of the Bay. The salinity ranges from 18.7 ppt to 36 ppt. (36 ppt is as salty as the ocean.)^[15]

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 rare for the surface of the Bay to freeze in winter, something that happened most recently in the winter of 1976–77.^[16]

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

The Chesapeake Bay is home to numerous fauna that either migrate to the Bay at some point during the year or live there year-round. There are over 300 species of fish and numerous shellfish and crab species. Some of these include the Atlantic menhaden, striped bass, American eel, eastern oyster, and the blue crab.^[17]

Birds include ospreys, great blue herons, bald eagles,^[18] and peregrine falcons, the last two of which were threatened by DDT; their numbers plummeted but have risen in recent years.^[19] The piping plover is a near threatened species that inhabits the wetlands.^[19]

Larger fish such as Atlantic sturgeon,^[20] varieties of sharks,^[21][22] and stingrays visit the Chesapeake Bay.^[23] The waters of the Chesapeake Bay have been regarded one of the most important nursery areas for sharks along the east coast.^[24] Megafaunas such as bull sharks, tiger sharks, scalloped hammerhead sharks, and basking sharks^[24] and manta rays are also known to visit.

Bottlenose dolphins are known to live seasonally/yearly in the Bay.^[25] There have been unconfirmed sightings of humpback whales in recent years.^[26][27] Endangered North Atlantic right whale^[28] and fin, and minke and sei whales have also been sighted within and in the vicinity of the Bay.^[23]

Although the Bay is farther north than its typical habitat range, a male manatee visited the Bay several times between 1994 and 2011. The manatee, recognizable due to distinct markings on its body, was nicknamed "Chessie" after a legendary sea monster that was allegedly sighted in the Bay during the 20th century.^[29][30][31] The same manatee has been spotted as far north as Rhode Island, and was the first manatee known to travel so far north.^[32] Other manatees are occasionally seen in the Bay and its tributaries, which contain sea grasses that are part of the manatee's diet.^[33]

Loggerhead turtles are known to visit the Bay.^[23]

The Chesapeake Bay is also home to a diverse flora, both land and aquatic. Common submerged aquatic vegetation includes eelgrass and widgeon grass. A report in 2011 suggested that information on underwater grasses would be released, because "submerged grasses provide food and habitat for a number of species, adding oxygen to the water and improving water clarity."^[34] Other vegetation that makes its home in other parts of the Bay are wild rice, various trees like the red maple, loblolly pine and bald cypress, and spartina grass and phragmites.^[35] Invasive plants have taken a significant foothold in the Bay; plants such as Brazilian waterweed, native to South America, have spread to most continents with the help of aquarium owners, who often dump the contents of their aquariums into nearby lakes and streams. It's highly invasive, and has the potential to flourish in the low-salinity tidal waters of the Chesapeake Bay. Dense stands of Brazilian waterweed can restrict water movement, trap sediment and affect water quality. Various local K-12 schools in the Maryland and Virginia region often have programs that cultivate native bay grasses and plant them in the Bay.

In 1524, Italian explorer Giovanni da Verrazzano, (1485–1528), in service of the French crown, (famous for sailing through and thereafter naming the entrance to New York Bay as the "Verrazzano Narrows", including now in the 20th century, a suspension bridge also named for him) sailed past the Chesapeake, but did not enter the Bay.^[38] Spanish explorer Lucas Vásquez de Ayllón sent an expedition out from Hispaniola in 1525 that reached the mouths of the Chesapeake and Delaware Bays. It may have been the first European expedition to explore parts of the Chesapeake Bay, which the Spaniards called "Bahía de Santa María" ("Bay of St. Mary") or "Bahía de Madre de Dios."("Bay of the Mother of God")^[39] De Ayllón established a short-lived Spanish mission settlement, San Miguel de Gualdape, in 1526 along the Atlantic coast. Many scholars doubt the assertion that it was as far north as the Chesapeake; most place it in present-day Georgia's Sapelo Island.^[40] In 1573, Pedro Menéndez de Márquez, the governor of Spanish Florida, conducted further exploration of the Chesapeake.^[38] In 1570, Spanish Jesuits established the short-lived Ajacan Mission on one of the Chesapeake tributaries in present-day Virginia.

The arrival of English colonists under Sir Walter Raleigh and Humphrey Gilbert in the late 16th century to found a colony, later settled at Roanoke Island (off the present-day coast of North Carolina) for the Virginia Company, marked the first time that the English approached the gates to the Chesapeake Bay between the capes of Cape Charles and Cape Henry. Three decades later, in 1607, Europeans again entered the Bay. Captain John Smith of England explored and mapped the Bay between 1607 and 1609, resulting in the publication in 1612 back in the British Isles of "A Map of Virginia".^[41] Smith wrote in his journal: "Heaven and earth have never agreed better to frame a place for man's habitation."^[42] The new laying out of the "Captain John Smith Chesapeake National Historic Trail", the United States' first designated "all-water" National Historic Trail, was created in July 2006, by the National Park Service of the U.S. Department of the Interior following the route of Smith's historic 17th-century voyage.^[43] Because of economic hardships and civil strife in the "Mother Land", there was a mass migration of southern English Cavaliers and their servants to the Chesapeake Bay region between 1640 and 1675, to both of the new colonies of the Province of Virginia and the Province of Maryland.

The Chesapeake Bay was the site of the Battle of the Chesapeake (also known as the "Battle of the Capes", Cape Charles and Cape Henry) in 1781, during which the French fleet defeated the Royal Navy in the decisive naval battle of the American Revolutionary War. The British defeat enabled General George Washington and his French allied armies under Comte de Rochambeau to march down from New York and bottle up the rampaging southern British Army of Lord Cornwallis from the North and South Carolinas at the siege of Battle of Yorktown in Yorktown, Virginia. Their marching route from Newport, Rhode Island through Connecticut, New York State, Pennsylvania, New Jersey and Delaware to the "Head of Elk" by the Susquehanna River along the shores and also partially sailing down the Bay to Virginia. It is also the subject of a designated National Historic Trail under the National Park Service as the Washington-Rochambeau Revolutionary Route.

The Bay would again see conflict during War of 1812. During the year of 1813, from their base on Tangier Island, British naval forces under the command of Admiral George Cockburn raided and plundered several towns on the shores of the Chesapeake, treating the Bay as if it were a "British Lake". The Chesapeake Bay Flotilla, a fleet of shallow-draft armed barges under the command of U.S. Navy Commodore Joshua Barney, was assembled to stall British shore raids and attacks. After months of harassment by Barney, the British landed on the west side of the Patuxent at Benedict, Maryland, the Chesapeake Flotilla was scuttled, and the British trekked overland to burn the U.S. Capitol in August 1814. A few days later in a "pincer attack", they also sailed up the Potomac River to attack Fort Washington below the National Capital and demanded a ransom from the nearby port town of Alexandria, Virginia.

There were so-called "Oyster Wars" in the late 19th and early 20th centuries. Until the mid-20th century, oyster harvesting rivaled the crab industry among Chesapeake watermen, a dwindling breed whose skipjacks and other workboats were supplanted by recreational craft in the latter part of the century.^[44]

In the 1960s, the Calvert Cliffs Nuclear Power Plant on the historic Calvert Cliffs in Calvert County on the Western Shore of Maryland began using water from the Bay to cool its reactor.

The Chesapeake Bay forms a link in the Intracoastal Waterway, of the bays, sounds and inlets between the off-shore barrier islands and the coastal mainland along the Atlantic coast connecting the Chesapeake and Delaware Canal (linking the Bay to the north and the Delaware River) with the Albemarle and Chesapeake Canal (linking the Bay, to the south, via the Elizabeth River, by the cities of Norfolk and Portsmouth to the Albemarle Sound and Pamlico Sound in North Carolina and further to the Sea Islands of Georgia). A busy shipping channel (dredged by the U.S. Army Corps of Engineers since the 1850s) runs the length of the Bay, is an important transit route for large vessels entering or leaving the Port of Baltimore, and further north through the Chesapeake and Delaware Canal to the ports of Wilmington and Philadelphia on the Delaware River.

During the later half of the 19th century and first half of the 20th century, the Bay was plied by passenger steamships and packet boat lines connecting the various cities on it, notably the Baltimore Steam Packet Company ("Old Bay Line").

In the later 20th century, a series of road crossings were built. One, the Chesapeake Bay Bridge (also known as the Governor William Preston Lane, Jr. Memorial Bridge) between the state capital of Annapolis, Maryland and Matapeake on the Eastern Shore, crossing Kent Island, was constructed 1949-1952. A second, parallel, span was added in 1973. The Chesapeake Bay Bridge-Tunnel, connecting Virginia's Eastern Shore with its mainland (at the metropolitan areas of Virginia Beach, Norfolk, Portsmouth, and Chesapeake), is approximately 20 miles (32 km) long; it has trestle bridges as well as two stretches of two-mile-long (3.2 km) tunnels that allow unimpeded shipping; the bridge is supported by four 5.25-acre (21,200 m2) man-made islands. The Chesapeake Bay Bridge-Tunnel was opened for two lanes in 1964 and four lanes in 1999.^[45][46]

Tides in the Chesapeake Bay exhibit an interesting and unique behavior due to the nature of the topography (both horizontal and vertical shape), wind driven circulation, and how the Bay interacts with oceanic tides. Research into the peculiar behavior of tides both at the northern and southern extents of the Bay began in the late 1970s. One study noted sea level fluctuations at periods of 5 days, driven by sea level changes at the Bay's mouth on the Atlantic coast and local lateral winds, and 2.5 days, caused by resonant oscillations driven by local longitudinal winds,^[47] while another study later found that the geometry of the Bay permits for a resonant period of 1.46 days.^[48]

A good example of how the different Chesapeake Bay sites experience different tides can be seen in the tidal predictions published by the National Oceanographic and Atmospheric Administration (NOAA) (see figure at right).

At the Chesapeake Bay Bridge Tunnel (CBBT) site, which lies at the southernmost point of the Bay where it meets the Atlantic Ocean near Norfolk, Virginia, and the capes of Charles and Henry, there is a distinct semi-diurnal tide throughout the lunar month, with small amplitude modulations during spring (new/full moon) vs. neap (one/three quarter moon) tidal periods. The main forcing of the CBBT tides are typical, semi-diurnal ocean tides that the East Coast of the United States experiences.

Baltimore, in the northern portion of the Bay, experiences a noticeable modulation to form its mixed tidal nature during spring vs. neap tides. Spring tides, when the sun-earth-moon system forms a line, cause the largest tidal amplitudes during lunar monthly tidal variations. In contrast, neap tides, when the sun-earth-moon system forms a right angle, are muted, and in a semi-diurnal tidal system (such as that seen at the CBBT site) this can be seen as a lowest intertidal range.

Two interesting points that arise from comparing these two sites at opposite ends of the Bay are their tidal characteristics - semi-diurnal tide for CBBT and mixed tide for Baltimore (due to resonance in the Bay) - and the differences in amplitude (due to dissipation in the Bay).

The Bay is mostly known for its seafood production, especially blue crabs,^[49] clams and oysters. In the middle of the 20th century, the Bay supported 9,000 full-time watermen, according to one account.^[49] 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 and in the Susquehanna River watershed), over-harvesting, and invasion of foreign species.

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 States still under sail power. Other characteristic bay-area workboats include sail-powered boats such as the log canoe, the pungy, the bugeye, and the motorized Chesapeake Bay deadrise, the state boat of Virginia.^[50]

In contrast to harvesting wild oysters, oyster farming is a growing industry for the Bay to help maintain the estuary's productivity as well as a natural effort for filtering impurities such as excess nutrients from the water in an effort to reduce the effects of man-made pollution. The Chesapeake Bay Program is using oysters to reduce the amount of nitrogen compounds entering the Chesapeake Bay.^[51]

Oysters are hermaphroditic and will change gender at least once during their lifetime, often starting as male and ending as female; there are numerous ways to cook and eat them, as well as recipes and sauces to accompany oyster dishes.^[44] One account:

The Bay is famous for its rockfish, a regional name for striped bass. Once on the verge of extinction, rockfish have made a significant comeback because of legislative action that put a moratorium on rockfishing, which allowed the species to re-populate. Rockfish can now be fished in strictly controlled and limited quantities.

The Chesapeake Bay is a main feature for tourists who visit Maryland and Virginia each year.^[52] Fishing, crabbing, swimming, boating, kayaking,^[18] 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.^[53] One report suggested that Annapolis was an appealing spot for families, water sports and boating.^[54] Commentator Terry Smith spoke about the Bay's beauty:

One account suggested how the Chesapeake attracts people:

In the 1970s, the Chesapeake Bay was found to contain one of the planet's first identified marine dead zones, where waters were so depleted of oxygen that 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 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 residential, farm and industrial waste throughout the watershed. One report in 2010 criticized Amish farmers for having cows that "generate heaps of manure that easily washes into streams and flows onward into the Chesapeake Bay".^[56]

The runoff and pollution have many components that help contribute to the algal bloom, which is mainly fed by phosphorus and nitrogen.^[57] 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 Chesapeake Bay, have shrunk by more than half there since the early 1970s. Overharvesting, pollution, sedimentation and disease have turned much of the Bay's bottom into a muddy wasteland.^[58]

One particularly harmful source of toxicity is Pfiesteria piscicida, which can affect both fish and humans. Pfiesteria caused a small regional panic in the late 1990s when a series of large blooms started killing large numbers of fish while giving swimmers mysterious rashes; nutrient runoff from chicken farms was blamed for the growth.^[59]

The Bay has improved slightly in terms of the overall health of its ecosystem, earning a rating of 31 out of 100 in 2010, up from 28 in 2008.^[2] An estimate in 2006 from a "blue ribbon panel" said cleanup costs would be $15 billion.^[42] Compounding the problem is that 100,000 new residents move to the area each year.^[42] A report in 2008 in the Washington Post suggested that government administrators had overstated progress on cleanup efforts as a way to "preserve the flow of federal and state money to the project."^[60] In January 2011, there were reports that millions of fish had died, but officials suggested it was probably the result of extremely cold weather.^[61]

While the Bay's salinity is ideal for oysters and the oyster fishery was at one time the Bay's most commercially viable,^[62] the population has in the last fifty years been devastated. Maryland once had roughly 200,000 acres (810 km2) of oyster reefs. Today it has about 36,000.^[62] 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.^[63] The harvest's gross value decreased 88% from 1982 to 2007.^[64] One report suggested the Bay had fewer oysters in 2008 than 25 years earlier.^[5]

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.^[62] 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.^[62] The Bay's oyster industry has also suffered from two diseases: MSX and Dermo.^[65]

The depletion of oysters 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 while his knees are still dry.

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. 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.^[66]

Efforts to repopulate the Bay 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 (32,000 m2) of the Trent Hall sanctuary.^[67] Scientists from the Virginia Institute of Marine Science at the College of William & Mary claim that experimental reefs created in 2004 now house 180 million native oysters, Crassostrea virginica, which is far fewer than the billions that once existed.^[68]

There are several magazines and publications that cover topics directly related to the Chesapeake Bay and life and tourism within the Bay region.

The Capital, a newspaper based in Annapolis, reports about news pertaining to the Western Shore of Maryland and the Annapolis area.^[69] Chesapeake Bay Magazine and PropTalk focus on powerboating, while SpinSheet focuses on sailing.^[70][71][72]

Singer and songwriter Tom Wisner recorded several albums, often about the Chesapeake Bay. The Boston Globe wrote that Wisner "always tried to capture the voice of the water and the sky, of the rocks and the trees, of the fish and the birds, of the gods of nature he believed still watched over it all."^[73] He was known as the Bard of the Chesapeake Bay.^[73]

The 1976 hit "Moonlight Feels Right" by Starbuck refers to Chesapeake Bay: "I'll take you on a trip beside the ocean / And drop the top at Chesapeake Bay."