Do you have a question about the Chesapeake Bay? Explore our list of frequently asked questions to learn more about the Bay and its watershed, habitats and wildlife. You can browse the FAQ by category, or explore the answers to some of our most common questions below.
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A bay is an inlet of the sea. An estuary is a partially enclosed body of water where fresh water and salt water meet. Some bays—like the Chesapeake—are estuaries.
There are at least 12 shark species that can be found in the Chesapeake Bay, but these species rarely pose a threat to human safety. Some—like the sandbar shark, sand tiger shark and smooth and spiny dogfish—are common, while others—like the bull shark, basking shark and bonnethead—are rare visitors.
A number of factors have contributed to the decline in the Chesapeake Bay’s oyster population, including over-harvesting, disease (like MSX and Dermo), sedimentation and poor water quality.
Blue crabs do not eat more to prepare to winter hibernation (like, for instance, a black bear might). While blue crabs are heavier in the fall, this is because the crabs have gone through several molts and grown in size.
Blue crabs have a rapid growth rate and short life span. Few blue crabs live longer than three years.
The Chesapeake Bay watershed spans six states and the District of Columbia. Within this watershed are several large cities, including Cooperstown, N.Y.; Harrisburg, Pa.; Baltimore, Md.; Washington, D.C.; and Norfolk, Richmond and Charlottesville, Va.
Captain John Smith was an English explorer who played a pivotal role in settling America. His contacts with Native Americans and his Chesapeake Bay travels, which he documented in maps and journals, drew attention to the region and helped educate and attract English colonists to America. Today, they provide excellent insight into the Bay’s natural history before Europeans settled the region.
The Susquehanna, Potomac, Rappahannock, York and James rivers are the five major rivers that flow to the Chesapeake Bay.
Oysters prefer brackish and salty water. A salinity range between 10-28 parts per thousand (ppt) provides the best conditions for oysters. Oysters can die if salinity drops below 5 ppt for extended periods of time.
Phytoplankton cannot swim on their own. Tides and currents move these tiny, single-celled plants from place to place.
A tributary is a stream or river that eventually flows into a larger body of water. For example, the James River is a tributary of the Chesapeake Bay.
An ecosystem is a complex set of relationships among animals, plants, habitats, people and non-living things. All parts of an ecosystem interact with and depend on each other in some way.
The Chesapeake Bay is about 200 miles long, stretching from Havre de Grace, Maryland, to Norfolk, Virginia. The Bay’s width varies from its narrowest point (3.4 miles across near Aberdeen, Maryland) to its widest point (35 miles across near the mouth of the Potomac River).
On average, the Chesapeake Bay is about 21 feet deep. However, most parts of the Bay are extremely shallow. A person who is 6 feet tall could wade through more than 700,000 acres of the Bay and barely get his or her hat wet. The Bay also has a few channels that are more than 100 feet deep, which provide important habitat for aquatic life and passageways for ships.
The Choptank, James, Nanticoke, Patapsco, Patuxent, Potomac, Rappahannock, Susquehanna and York rivers are just a few of the many rivers that flow into the Chesapeake Bay. These rivers are fed by hundreds of thousands of streams and creeks that flow throughout the Chesapeake Bay watershed.
Anadromous fish live in the ocean, but must migrate to freshwater rivers and streams to spawn. American shad is one type of anadromous fish that lives in the Chesapeake Bay region.
Visit the EPA’s Surf Your Watershed page, where you can enter your zip code to find out what watershed(s) you live in.
Altogether, more than 100,000 streams, creeks and rivers thread through the Chesapeake Bay watershed.
More than 17 million people live in the Chesapeake Bay watershed.
A subwatershed is a small watershed contained within the larger Chesapeake Bay watershed. Each of the streams, creeks and rivers in the Bay watershed has its own watershed. For example, the Potomac River watershed is a subwatershed of the Chesapeake Bay watershed.
A watershed is an area of land that drains to a particular river, lake, bay or other body of water.
The Chesapeake Bay watershed stretches across more than 64,000 square miles.
Benthos are organisms that live on and in the bottom sediments of the Chesapeake Bay and its streams and rivers. Benthic communities are complex and include a wide range of animals, plants and bacteria from all levels of the food web.
Epifauna and infauna are both types benthic, or bottom-dwelling, organisms. Epifauna live attached to a surface and infauna live within the Bay’s bottom sediments.
Phytoplankton populations in the Bay are an excellent indicator of nutrient pollution, as well as efforts to reduce pollution. Phytoplankton respond quickly to changes in nutrient levels, which gives researchers a good indication of the Bay’s health.
Plankton form the base of the Chesapeake Bay food web. All fish and shellfish depend on plankton for food during the early part of their lives, and some consume plankton their entire lives.
Zooplankton are free-floating animals. They are the most plentiful animals in the Bay and its rivers. Zooplankton are mostly microscopic, but can range in size from single-celled protozoa to large jellyfish. Zooplankton form a link between the phytoplankton community and larger species at higher levels in the food web.
Phytoplankton (or algae) are tiny, single-celled plants. They are the primary producers of food and oxygen in the Chesapeake Bay, forming the base of the food web.
Scientists use a small, long, hand-held device called a refractometer to measure salinity.
The Chesapeake Bay’s overall average salinity ranges from 13-17 parts per thousand (ppt), although salinity in the Bay varies widely depending on location, weather and season.
Fresh water enters the Chesapeake Bay primarily from its rivers and streams. Fresh water also enters via rain, snow and groundwater.
Salt water enters the Chesapeake Bay from the Atlantic Ocean, at the mouth of the Bay near Hampton Roads, Virginia.
In general, the lower Chesapeake Bay is salty and the upper Bay is fresh. Salinity gradually decreases as you move north and increases as you move south.
The Chesapeake Bay’s salinity ranges from fresh water (less than 0.5 parts per thousand) to salt water (25-30 ppt). The Bay's salinity is highest at its mouth, where water from the Atlantic Ocean enters. The water at the head of the Bay is fresh. The water in the middle portion of the Bay is brackish: a mixture of salt and fresh water.
The Chesapeake Bay’s salinity gradually decreases as you move north and increases as you move south. Salinity also varies widely from season to season and from year to year, depending on the amount of fresh water flowing from the Bay’s rivers.
The water at the mouth of the Chesapeake Bay is salty because it is mostly made up of salty water from the ocean. As you move north in the Bay, the water becomes less salty. Most of the Bay is brackish (a mixture of fresh and salty water).
The Chesapeake Bay is saltiest at its mouth, near Hampton Roads, Virginia. This is where salty ocean water comes into the Bay. The Bay’s salinity decreases as you move north.
Salinity is a measure of the amount of dissolved salts in the water. Water can be fresh, salty or brackish (a mixture of salt and fresh water).
The Chesapeake Bay is the largest of more than 100 estuaries in the United States.
Estuaries are among the most productive environments on earth, creating more organic matter each year than similarly-sized forests and agricultural areas. Estuaries also provide diverse habitats for wildlife and aquatic life, protect our communities against flooding, reduce pollution to waterways, and support local economies through commercial and recreational activities.
An estuary is a partially enclosed body of water where fresh water from streams and rivers mixes with salt water from the ocean. Some river mouths are estuaries. For example, the tidal portion of the Hudson River in New York is an estuary.
An estuary is a partially enclosed body of water where fresh water from streams and rivers mixes with salt water from the ocean. The Chesapeake Bay is an estuary.
Fish consumption advisories are public health notices that warn people about possible health risks from eating fish and shellfish from certain waterways.
Fish passageways allow shad and other anadromous fish to pass over dams and reach their upstream spawning grounds. There are five major fish passageway designs used in the Chesapeake Bay watershed: denil, steeppass, vertical slot, pool and weir, and fish lifts.
Dams block shad and other anadromous fish from reaching their upstream spawning grounds. Historically, most shad and river herring spawned in freshwater areas that are now upstream of dams, road culverts and other blockages.
Fish passage is the ability of fish to migrate up rivers, streams and other waterways, often to access spawning or rearing areas. Barriers to fish passage (which can include road culverts, dams, dikes and other obstructions) can reduce the distribution and habitat available to anadromous fish and, in some cases, eliminate fish populations altogether.
American shad are not listed as an endangered species. However, populations along the East Coast are very low.
Shad are anadromous, which means they migrate from the ocean to spawn in freshwater rivers and streams.
Shad spend most of their lives in the ocean. They migrate to freshwater rivers and streams to spawn. After hatching, young shad slowly migrate downstream, eventually leaving the Chesapeake Bay for the ocean.
There are many low-impact development techniques that can be installed around homes and buildings. Rain gardens, porous pavement and green roofs are a few techniques that will help reduce pollution from developed areas.
Global warming has led to sea level rise and increased temperatures in the Chesapeake Bay region and throughout the world. Other possible effects of global warming include habitat loss, increased precipitation and changes in wildlife patterns.
Blue crabs are omnivores. They will eat nearly anything they can find, including bivalves, crustaceans, dead fish, bristle worms, detritus, and even other crabs!
Best management practices (BMPs) are agricultural conservation practices that farmers use to reduce nutrient and sediment pollution while maintaining productive farming operations. Some common agricultural BMPs include cover crops, forest buffers, manure storage areas and rotational grazing.
An airshed is an area of land where pollution released into the air can eventually wind up in a specific water body. Airsheds can be very large. For example, the Chesapeake Bay’s nitrogen oxide (NOx) airshed is 570,000 square miles, stretching west to Ohio and north to Canada.
Poor water clarity does not allow sunlight to reach bay grasses growing at the bottom of shallow waters. These underwater grasses provide food and habitat for many animals, including fish, crabs and birds. Without bay grasses, these animals may not have the food and habitat they need to survive.
Water clarity improves when less pollution washes off the land and into streams, rivers and the Chesapeake Bay. You can help improve water clarity by fertilizing your lawn less and planting a buffer of trees and shrubs around your property. Also, when boating, make sure you obey wake laws so you don’t stir up bottom sediments in shallow areas.
Scientists use a device called a Secchi disc to measure water clarity. A Secchi disc is a simple, black-and-white circle attached to a rope. The Secchi disc is lowered into the water until it disappears, then pulled up until it can just barely be seen. Scientists note the water line on the rope and measure the distance between the Secchi disc and the water line. The measurement is the water’s clarity: the depth that sunlight is able to penetrate through the water.
Poor water clarity is usually caused by a combination of suspended sediments, organic matter and excess nutrients that fuel the growth of water-clouding algae. Weather also plays a large role in water clarity. Rain storms can wash dirt and pollutants into the Bay and cause the water to look muddy. During drier conditions, the water is usually clearer.
Some fish and crabs may be able to swim away from areas without enough oxygen. But other animals – such as oysters, clams and worms – are not able to swim away, and can die if there is not enough oxygen around them.
Scientists usually use an electronic dissolved oxygen meter to measure the amount of oxygen in the water.
Like all other species in the Chesapeake Bay, blue crabs need oxygen to survive. In rare cases, blue crabs have been known to come out of the water onto land to escape oxygen-deprived waters. This phenomenon is known as a “crab jubilee.”
Oxygen gets into the water when:
Sometimes the Bay’s deeper waters have little or no oxygen while surface waters have more oxygen. This usually happens in summer because of a combination of factors, including temperature, nutrient pollution, the way water flows in the Bay, and the shape of the Bay’s bottom.
Scientists generally agree that the Bay’s creatures need dissolved oxygen concentrations of 5.0 mg/L or more to live and thrive. However, the amount of oxygen an animal needs varies depending on how large or complex the animal is and where it lives.
Temperature, nutrient pollution, the way water flows in the Bay, and the shape of the Bay’s bottom all interact with each other to affect the amount of oxygen in the water.
A “dead zone” is a term often used to describe an area of the Chesapeake Bay that does not have enough dissolved oxygen to support life. Each summer, the Bay has a dead zone where fish, crabs and other animals cannot live because there is not enough oxygen in the water.
Just like humans, all of the Chesapeake Bay's living creatures – from the fish and crabs that swim through its waters to the worms that bury themselves in its muddy bottom – need oxygen to survive.
Dissolved oxygen is the amount of oxygen that is present in the water.
Historians are not sure of the true meaning of the name Chesapeake. It is usually cited as deriving from the Algonquin word chesepiooc, meaning “great shellfish bay.” But records from the 1580s refer to the Bay as chesapiock or chesapiuck, meaning “people on the great river.”
The Chesapeake Bay watershed includes parts of six states – Delaware, Maryland, New York, Pennsylvania, Virginia and West Virginia – and the entire District of Columbia.
Bay grasses are a critical part of the Chesapeake Bay ecosystem. Without bay grasses, underwater creatures such as fish and blue crabs do not have the shelter they need to survive, and migratory waterfowl do not have enough food to eat.
Another important role of bay grasses is to hold bottom sediments in place. If bay grasses are gone, waves can stir up bottom sediments and make the water cloudy. This can affect bay grass beds growing in other areas because they need clear water to survive.
People contribute pollution that can cloud the water and block sunlight from reaching bay grasses. This pollution comes from many sources, including farms, sewage, fertilizer and development.
Bay grasses usually die because the water is too cloudy for sunlight to reach them. Cloudy water is most often caused by pollution from excess nutrients and sediment. Extreme temperatures and certain human activities can also cause bay grasses to die.
Just like any other plant, bay grasses go through photosynthesis, so they need sunlight to grow. This means that the water that bay grasses grow in must be clear enough for the sun’s rays to pass through.
Bay grass beds form communities that provide food and shelter for many species. Fish, crabs and other animals visit bay grass beds to seek out food and find shelter from larger predators. Bay grasses are also an important source of food for waterfowl such as ducks and geese.
People can help save bay grasses by reducing the amount of pollution they contribute to the Chesapeake Bay and its rivers. Three ways you can pollute less are to fertilize your lawn less, plant a buffer of trees and shrubs around your property, and maintain your septic system (if you have one). Also, when boating, make sure you don’t disturb bay grass beds in shallow areas.
Extreme temperatures can have a negative effect on some bay grasses. For example, eelgrass cannot grow in water that is too warm. In 2005, very high temperatures caused large areas of eelgrass in the lower Chesapeake Bay to die. Other species of bay grasses react positively to high temperatures and grow more quickly when the water is warmer.
About 20 species of bay grasses grow in the Chesapeake Bay and in lakes, streams, reservoirs and other bodies of water throughout the Bay watershed.
Pfiesteria piscicida is a toxic microorganism linked to fish kills and lesions in several Chesapeake Bay rivers in 1997. Medical evidence at the time strongly suggested that human exposure to an active Pfiesteria outbreak may result in health effects. As a precaution, Maryland closed all affected rivers until the outbreaks ceased. However, there is no evidence that Pfiesteria toxins accumulate in fish flesh or that they can be passed to humans by eating seafood.
Since 1997, no major Pfiesteria outbreaks have been reported in the Bay region. Scientists continue to research the microorganism to determine how it produces toxins.
Bay grasses are a critical part of the Chesapeake Bay ecosystem because they provide food and habitat for countless species. They also help keep the water clear and healthy by absorbing nutrients, trapping sediments, reducing erosion and adding oxygen.
Bay grasses are plants that grow underwater in the Chesapeake Bay’s shallows. Bay grasses are also known as submerged aquatic vegetation or SAV.
SAV stands for submerged aquatic vegetation. SAV is more commonly known as bay grasses.
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