Earth and sky, woods and fields, lakes and rivers, are all excellent schoolmasters. They teach us more than we can learn from books.
— John Lubbock


Exploring a tidal flat in Galveston Bay. A new Hampshire salt marsh- Piscataqua Region.

Association of National Estuary Programs

Estuary Facts

What is an estuary?

Lower Columbia River

An estuary is a partially enclosed body of water along the coast where freshwater from rivers and streams meets and mixes with salt water from the ocean. Estuaries and the lands surrounding them are places of transition from land to sea and freshwater to salt water. Although influenced by the tides, they are protected from the full force of ocean waves, winds, and storms by barrier islands or peninsulas.

Estuaries are among the most productive ecosystems in the world. Many species of animals rely on the sheltered waters of estuaries for food, secure places to breed and migration stopovers. Coastal communities also rely on estuaries for food, recreation, jobs and shoreline protection. Of the 32 largest cities in the world, 22 are located in estuaries.

Many different habitat types are found in and around estuaries, including shallow open waters, freshwater and salt marshes, swamps, sandy beaches, mud and sand flats, rocky shores, oyster reefs, mangrove forests, river deltas, tidal pools, and seagrasses.


Why are estuaries important?

Partnership for the Delaware Estuary

Estuaries provide us with a suite of resources, benefits and services. Some of these can be measured in dollars and cents, but the total value is difficult to calculate. Estuaries provide places for diverse recreational activities, scientific study, environmental education, and aesthetic enjoyment. Estuaries are an irreplaceable natural resource that must be managed carefully for the benefit of everyone that value the resources and lifestyles they support.

Thousands of species of birds, mammals, fish, and other wildlife depend on estuarine habitats as places to live, feed, and reproduce. Many marine organisms, including most commercially-important species of fish, depend on estuaries at some point during their juvenile development. Because they are biologically productive, estuaries provide ideal areas for migratory birds to rest during their long journeys. Because many species of fish and wildlife rely on the sheltered waters of estuaries as protected spawning places, estuaries are often called the “nurseries of the sea.”

Estuaries have important commercial value and their resources provide economic benefits for tourism, fisheries and recreational activities. The protected coastal waters of estuaries also support important public infrastructure, serving as harbors and ports vital for shipping and transportation.

Estuaries also perform other valuable services. Water draining from uplands carries sediments, nutrients, and other pollutants to estuaries. As the water flows through wetlands such as swamps and salt marshes, much of the sediments and pollutants are filtered. This filtration process creates cleaner and clearer water, which benefits people and aquatic life. Wetland plants and soils also act as natural buffers between the land and ocean, absorbing flood waters and dissipating storm surges. This protects upland habitat as well as valuable real estate from storm and flood damage. Salt marsh grasses and other estuarine plants also help prevent erosion and stabilize shorelines.


Long Island Sound Estuary Program

Why protect estuaries?

The economy of many coastal areas is based primarily on the natural beauty and bounty of estuaries. There is a strong relationship between healthy ecosystems and strong regional economies given the large number of individuals that work within estuarine watersheds. More than half of the U.S. population lives in coastal areas, which includes estuaries. Coastal watershed counties provided 69 million jobs and contributed $7.9 trillion to the Gross Domestic Product in 2007 (National Ocean Economics Program, 2009).

Coastal counties are growing three times faster than counties elsewhere in the nation. Unfortunately, the increasing concentration of people upsets the natural balance of estuarine ecosystems and creates additional pressure. What happens on the land affects the quality of the water and health of all life that depend on estuaries. For example, rivers or streams that flows through an agricultural area pick up fertilizer, manure, and pesticides with rain runoff. As it passes through urbanized areas, the runoff also collects fertilizers and pet waste that wash off lawns, untreated sewage from failing septic tanks, wastewater discharges from industrial facilities, sediment from construction sites, and runoff from impervious surfaces like parking lots. The total pollution impacts on the quality of the water and the overall vitality and health of the entire ecosystem.

Thank you to the U.S. Environmental Protection Agency for providing information for this summary. Visit the EPA Website to learn more.