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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In general, nutrients like nitrogen and phosphorous reach the Chesapeake Bay from three sources: wastewater treatment plants; urban, suburban and agricultural runoff; and air pollution. Nutrients can also come from natural sources, like soil, plant material and wild animal waste.
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.
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 deepest part of the Bay is 174 feet deep.
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.
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.
Because phytoplankton respond quickly to changes in nutrient levels, their population density acts as an indicator of nutrient pollution and Bay 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.
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.
Nutrient and sediment pollution are the main causes of the Chesapeake Bay’s poor water clarity. Nutrients fuel the growth of water-clouding algae blooms, while particles of sediment can float in the water. Weather also plays a role in water clarity: rain storms wash dirt and pollutants into the Bay, muddying the water.
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.
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.
Underwater 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.
Extreme temperatures can have a negative effect on some underwater 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 grasses react positively to high temperatures and grow more quickly when the water is warmer.
Underwater grasses are a critical part of the Chesapeake Bay ecosystem. Without them, 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 underwater grasses is to hold bottom sediments in place. If they are gone, waves can stir up bottom sediments and make the water cloudy. This can affect grass beds growing in other areas, because they need clear water to survive.
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