Page Contents:

What is an Estuary?


Zones of an Estuary

Salt Marshes, Seagrass, and Mangroves

Why are Estuaries Important?

Education, Food Production, Supports the Economy, Supports Life, Preserves Culture, Blue Carbon, Filtration, Storm Buffering 


What is an Estuary?

An estuary is a partially enclosed body of water formed by fresh water from rivers flowing into and mixing with ocean saltwater. Often, the fresh water is prevented from flowing into the open ocean by land masses such as peninsulas, islands, or surrounding salt marshes. This makes estuaries unique environments that sustain a diverse biological community of plants and animals. Some of the most commonly known estuaries in the United States are the Chesapeake Bay, Puget Sound, and the Indian River Lagoon.


Zones of an Estuary

 Estuaries can be divided into three zones: 

Supratidal Zone Intertidal Zone Subtidal Zone
Area above high tide that extends into higher lands. This is also known as the splash zone.  Area that is covered during high tide and barren during low tide. Often includes rocky cliffs and mud flats. There are very few organisms that are resilient enough to live in this harsh environment. Also known as the littoral or transition zone. Area that extends past the low tide line into open waters. This area is continuously covered by water. 
Organisms: Algae, fungi, snails, barnacles. Organisms: Crabs, barnacles, mussels, shrimps, snails, sea urchins.  Organisms: fish, marine organisms, crabs.  


The zones of an estuary. (Diagram from Taking Nature's Pulse: Section 2: B.C.'s Natural Legacy) 



Salt Marshes, Seagrass, and Mangroves

Coastal habitats can vary depending on geographic region. The three main types of estuary habitats include Salt Marshes, Seagrass, and Mangroves. RAE works to restore all of these habitats in order to preserve a kind of ecosystem that has brought tranquility, education, and jobs to millions of people all over the country. 
Salt marshes are coastal wetlands dominated by grass and shrub plants. Salt marshes are often characterized by having very high salinity (salt content) and sporadic small islands. Organisms that live here must withstand harsh environments due to rapidly changing tides and salinity. In addition to providing key marine habitat, salt marshes help to filter pollutants, stabilize the shoreline, serve as a buffer to storms and flooding, and sequester and store large amounts of  
Seagrass (or submerged aquatic vegetation) habitats are constantly submerged, and consist of aquatic grasses, providing food and shelter to many aquatic species. They include, but are not limited to, fish, crabs, manatees and sea turtles. Sea grasses are very sensitive to water pollution and changes in pH.   
Mangroves are a type of tropical forest found in coastal areas that are regularly flooded by tidal water. They are among the most carbon-rich forests in the tropics and provide many ecosystem services. They provide spawning grounds for fish species, filter pollutants from coastal waters, and protect coastal development and communities against storms, floods and erosion. These unique evergreen plants can withstand high salinity and harsh environments.

Food Production

Healthy estuaries produce more food per acre than the richest Midwestern farmland because of the fertile mix of nutrients from land and sea. Most fish and shellfish complete part of their life cycle in an estuary. Salmon, atlantic menhaden, herring, and striped bass are a couple of the fish that use estuaries for a part of their lifecycle.

Supports Life

Beyond providing food for our consumption, estuaries provide critical habitat for thousands of species of fish, birds, plants, and animals that depend on healthy habitat for their survival. There are many estuarine species on the endangered or threatened species list. Some of these include: the american alligator, the loggerhead sea turtle, and the manatee.

Supports the Economy

There are over 30 million jobs in the fishing, tourism and recreational boating industries -- all of which depend on healthy estuaries for their products and customers. Indeed, estuaries and coastal waters provide essential habitat for 75% of America's commercial fish catch and 80 to 90% of the recreational fish catch. The total fish catch in estuaries contributes $4.3 billion a year to the U.S. economy (ANEP, 1998).

Estuaries are also important sites for transportation and international or domestic commerce. Commercial shipping employs around 50,000 people. Coastal recreation can generate up to 12 million dollars per year. These are only a couple of the hundreds of economic contributions made by estuaries.

Preserves Culture

Healthy estuaries support unique, centuries-old cultures, traditions and ways of life dependent upon the diversity of wildlife for everything from livelihoods to storytelling. Estuary restorations will maintain these ways of life -- and the heritage they embody -- for the benefit of future generations.

In addition, approximately 70% of the American  population visit estuaries and coastal areas every year for vacations, recreation, sport, or sightseeing.  The more we do to restore estuaries, the more Americans will be able to experience their amazing bounty.

Of the 32 largest cities in the world, 22 are located on estuaries. For the 110 million Americans who live near estuaries, they are linchpins in people's quality of life: for their scenic beauty, for their recreational opportunities, for their bounty, for their abundance of life and for their mere presence. Restoring estuary habitat is the only way to ensure that this quality of life is protected and improved.

Blue Carbon

Coastal wetlands also remove and store large amounts of carbon - an ecosystem service referred to as "blue carbon." To learn more about blue carbon and how wetlands mitigating climate change can benefit coastal restoration and conservation efforts, visit our blue carbon webpage.

Filtration and Storm Buffering

Estuaries are important filters of pollutants that come from the surrounding watershed. The organisms in estuaries can help to remove pesticides, sediments, and excess nutrients from industrial or residential runoff. Estuaries can filter out these pollutants before they enter into the ocean. As a result, estuaries can be very polluted bodies of water, but also some of the most fertile.

Estuaries also act as storm buffers to the mainland, protecting residential areas from harsh storms such as hurricanes. During a surge, or rise of water due to a storm, a coastal estuary can absorb extra water and its energy without damaging its environment. They can also help to protect against coastal erosion. 


Estuaries are a matchless educational resource that must be maintained as living laboratories of life. As one of the most biologically diverse ecosystems in America, the opportunities for learning are endless. In order to secure these educational opportunities for future generations, restoring and protecting estuaries is essential.