Environmental Factors


Human Impact

Nearly 17 million people live in the Chesapeake Bay watershed, and demographers estimate that the watershed's population is growing by about 157,000 residents per year. At this rate, the population will reach 20 million by 2030. A growing population creates issues that threaten the Bay ecosystem.

Land use changes

As people move to the area and development increases, land use in the watershed changes. New homes, businesses, and roads replace forests and fields. Lands that once absorbed rainfall have been transformed into impervious surfaces such as parking lots and roads that increase stormwater runoff—often full of sediment, excess nutrients, and chemical contaminants—flowing into the Bay and its tributaries.

More people also means more cars on the road, increasing traffic congestion as well as air pollution.


Air pollution threatens the air we breathe and the land and water. Air and water pollution are intricately linked. Of particular concern to the Chesapeake region are airborne nitrogen and chemical contaminants such as mercury. These airborne pollutants come from large point sources like power plants and industrial facilities, vehicles, and agricultural sources. Airborne nitrogen increases the acidity of surface waters and soils, forms ground-level ozone, and contaminates drinking water. Chemical contaminants persist in the environment, moving through the food web in a process called bioaccumulation. This affects the growth and reproduction of both terrestrial and aquatic species.

Excess nutrients

Nitrogen and chemical contaminants pose threats to the Chesapeake Bay when they enter the Bay either by falling directly into the water or by falling onto the land and being carried into the water by stormwater runoff. Excess nutrients such as nitrogen and phosphorus—most of which come from agricultural sources such as fertilizer and manure—create algae blooms that prevent sunlight from reaching submerged aquatic vegetation, limiting growth of vital underwater Bay grasses. These excess nutrients also deplete dissolved oxygen, necessary for the survival of oysters, crabs, and other bottom-dwelling species in the Bay.


Excess sediments also contribute to the Bay's poor health. More than 18.7 billion pounds (8.5 billion kg) of sediment enter the Bay each year. Sediments come from the erosion of land and stream banks (watershed sources) and shoreline and nearshore areas (tidal sources). Too much sediment makes the water cloudy, which keeps sunlight from reaching underwater grasses; smothers oysters and other bottom-dwelling species; degrades streams; clogs ports and channels; and binds with pollutants, which then spread throughout the Bay.


The fishing industry is essential to the Chesapeake Bay character and economy. The Bay provides rich grounds for both commercial and recreational fisheries of the Chesapeake's signature species, including blue crabs, oysters, American shad, Atlantic menhaden, and striped bass. Overfishing, along with pollution, diseases, and other stressors, has affected the populations of many fish and shellfish in the Bay and, in cases like the American shad, contributed to closures of commercial fisheries in the Bay.

Invasive species

Plants and animals currently living and reproducing in a habitat outside their historic native range are considered "exotic." Exotic species become "invasive" when they negatively impact an ecosystem or species by encroaching on habitat and food sources. Introduced through a variety of means (some intentional, some not), invasive plants, insects, and diseases threaten all the habitats of the watershed. Invasive plants often grow and reproduce faster than native species, lowering the quality of available food and shelter for native species and out-competing native plants for habitat and pollinators.


The Bay Today

Increasing temperatures

The Chesapeake region has begun to feel the effects of a changing climate, which has repercussions for the entire ecosystem. Over the last century, the average air temperature along the coastal margins of the Chesapeake Bay has warmed 1.4° F. Between 1950 and 2000 water temperatures rose about 2° F. These warmer air and water temperatures can change the plant and animal species in an area, contribute to expanding dead zones and algal blooms, and encourage the expansion of hardy invasive species such as nutria.


Much of the Chesapeake region is experiencing greater precipitation extremes and a 10 percent increase in average precipitation. The increasing precipitation and storm intensities will lead to greater volumes of runoff and associated toxic chemicals and nutrient pollution in Bay waters.

Precipitation is part of the water cycle, also known as the hydrologic cycle—the movement of water on, above, and below the surface of the Earth.

Sea-level rise

Water levels in the Bay have also risen, with nearly a foot of sea-level rise in some places. Many coastal marshes and small islands have already been lost to rising water, and more are at risk. These marshes provide important ecosystem functions by filtering pollution, protecting shorelines, and providing habitat. Sea-level rise will also affect salinity and distribution of freshwater in the estuary—and consequently the Bay's animals and plants.

Effects on waterfowl

Global warming poses a triple threat to waterfowl in the Chesapeake Bay. First, the summer breeding grounds of many of the Bay's migratory duck species are threatened. Many of these birds breed in the Prairie Pothole Region of south-central Canada and north-central United States, which has an abundance of small, shallow wetlands. With 50 percent of the nation's ducks coming from this area, it is the most important breeding ground for North America's migratory ducks. As the climate warms, these vital wetlands are expected to remain wet for shorter periods or dry up all together.
Second, as global temperatures increase, some migrating waterfowl have begun a phenomenon known as "shortstopping." Many of the birds that formerly spent the winter in the Chesapeake Bay watershed are stopping farther north along their routes as they find more ice-free areas as winters become warmer.

A third threat to the migrating waterfowl will affect those who do make it to their wintering grounds in the Chesapeake. They will likely face a loss of shallow-water habitat as sea levels rise. Higher water levels will inundate the coastal marshes and wetlands that provide vital food for these animals.

Effects on fish and shellfish

Researchers have linked the spread of new diseases and more frequent epidemics to global warming. In the Chesapeake, a new species of mycobacterium recently infected rockfish, and outbreaks are more common in other Bay fish as well. Diseases have decimated native oysters. Poor water quality, pollution, and habitat degradation are factors in these infections, but the stress of warmer water makes the species more vulnerable to disease.

Effects on submerged aquatic vegetation

Resource managers expect sea-level rise to have a direct effect on submerged aquatic vegetation in the Chesapeake Bay. As water depth increases, the sunlight available to the plants decreases, reducing their ability to photosynthesize. Higher water temperatures also affect underwater grasses. For example, higher water temperatures, in conjunction with turbidity and low-light conditions, have contributed to the decline of eelgrass in the last decade. Warmer water, in conjunction with turbidity and low-light conditions, kills the grasses. Some documentation indicates that grasses can recover when water conditions improve, but the trend towards further warming will have the opposite effect.

Increased precipitation as a result of climate change alters the amount of water flowing into the Bay, which, in turn, can decrease salinity as more freshwater runoff pours into the Bay. This change in salinity can have a dramatic effect on available habitat for submerged aquatic vegetation. Additionally, species have different abilities to tolerate salinity, so the species that are present may change.

Additional Information

Climate Change and Your National Parks

Top of Page



Restoring the Bay

Today the Chesapeake Bay is in peril. We can see the results of human activities and natural events that affect the Bay's health and diversity. The Bay's ability to sustain life has diminished in visible and measurable ways. Key species have declined, threatening the sensitive ecosystem and the livelihoods of communities dependent on Bay harvests. Cutting forests to make way for development has destroyed natural protections for fragile shorelines, habitats, and water quality. The complex network of rivers and streams within the surrounding watershed carries pollution and heavy sediment loads downstream.

From historical accounts left by early explorers, we know how abundant the Chesapeake Bay once was. Through modern science, we know what actions are needed to restore it to health. Through concerted restoration efforts involving all levels of government and countless organizations and individuals, we can see progress. But restoring the Chesapeake Bay is a race against time. Population growth and other human activities are offsetting much of the recent restoration progress. The future health of the Bay depends on accelerating restoration efforts and involving every person who lives in or visits the watershed.

Partner Efforts

The Chesapeake Bay was the nation's first estuary targeted by the U.S. Congress for restoration and protection. In the 1970s Congress authorized a five-year study to analyze the rapid loss of wildlife and aquatic life that was devastating the Bay. The findings of this study led to creation of the Chesapeake Bay Program in 1983 to head the restoration of the Bay and its tributaries.

The Chesapeake Bay Program (CBP) is a regional partnership that includes Delaware, Maryland, New York, Pennsylvania, Virginia, West Virginia, and the District of Columbia; the Chesapeake Bay Commission (a tri-state legislative body representing Maryland, Virginia, and Pennsylvania); the U.S. Environmental Protection Agency; and more than two dozen other federal agencies. The National Park Service is a partner in this effort. The National Park Service administers the Chesapeake Bay Gateways and Watertrails Network to help people experience the Chesapeake Bay and understand how to become involved in protecting and restoring this national treasure.

Partners in the Chesapeake Bay Program pledge to work together to reduce pollutants going into the Bay and to restore its living resources. In 1987 the CBP Executive Council set a goal to reduce nitrogen and phosphorus entering the Bay by 40 percent by the year 2000. At the time, setting numeric goals with specific deadlines was unprecedented, but the practice has become a hallmark of the Chesapeake Bay Program.

The Chesapeake Bay Program identifies specific measures to quantify the effectiveness of restoration efforts. You can see an annual assessment of Bay health and restoration at the Chesapeake Bay Program website.

The Chesapeake Bay Program tracks 19 reporting-level indicators grouped into five priority areas that represent major elements of the Bay restoration efforts: reducing pollution, restoring habitats, managing fisheries, protecting watersheds, and fostering stewardship.

Quantitative goals have been set for each indicator. The Chesapeake Bay Program tracks progress toward the overall goal of a fully restored Chesapeake ecosystem—a goal of 100 percent. Recent assessments show that while progress has been made in some areas, the Bay remains in poor condition, and restoration efforts must be accelerated.

Fortunately federal and state partners are not alone in this effort. On-the-ground activities are occurring throughout the 64,000-square-mile watershed to accelerate restoration progress. Hundreds of nonprofit organizations are actively working to restore and conserve natural resources. These watershed organizations are essential partners in restoring and preserving a healthy Chesapeake Bay.
The Chesapeake Bay Program and its many partners are working to restore the balance between the needs of the region's people and the needs of the Chesapeake Bay ecosystem for clean water and ample habitat for aquatic life. Ultimately, the success of these efforts depends on the active participation and commitment of everybody who lives in or visits the Chesapeake Bay watershed. The nearly 100,000 rivers and streams running through the watershed act like pipelines into the Chesapeake. What people do in their local watershed affects the interrelated parts of the ecosystem. Fostering citizen stewardship is a top priority for CBP partners. For the Bay to be restored and protected, the region's citizens must be committed to helping solve the Bay's problems.

What you can do

You may think you have little impact on the Chesapeake Bay, but collectively the nearly 18 million people living in the Chesapeake watershed play a very significant role in the health of the Bay and its many tributaries. It will take the actions of all of us to successfully restore the Chesapeake. Simple everyday actions make a big difference if we each do our part to save the Bay.

Last updated: August 8, 2018

Park footer

Contact Info

Mailing Address:

1750 Forest Drive
Suite 140

Annapolis, MD 21401


410 260-2470

Contact Us

Stay Connected