What is an estuary?

An estuary is a partially enclosed body of water along the coast where freshwater from land 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. A large variety of species of fish, birds, crabs, shellfish and other wildlife rely on the sheltered waters and use estuaries for feeding, nesting, breeding, nursery areas, 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.

Kayaking in the estuary.

Why are estuaries important?

Estuaries provide us with a suite of resources, benefits and services; sustaining vibrant economies and healthy coastal communities. Some of these benefits can be measured in dollars and cents, but the total value of an estuary is difficult to calculate. Estuaries support water-dependent and water-related industries and 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 values 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 depend on estuaries at some point during their juvenile development; it is estimated that more than 600 commercial fish species spend some part of their lives in an estuary.   More than 80 percent of all fish and shellfish species use estuaries as primary habitat or as a spawning or nursery ground. Estuaries are often called the “nurseries of the sea” because many species of fish and wildlife rely on the sheltered waters of estuaries as protected spawning places. These thriving ecosystems also serve as a stopover point for migratory birds to take a rest and eat before continuing their long journeys.

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. Coastal watershed counties provided 69 million jobs and generated $7.9 trillion Gross Domestic Product (GDP), half of the nation’s total GDP for 2007 (National Ocean Economics Program, 2009).

Healthy 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, nutrients are recycled and 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 energy. 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.

Why protect estuaries?

Our estuaries are a vital part of our natural infrastructure, providing multiple benefits to our economy. 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 and live within estuarine watersheds. Today more than 52 percent of the nation’s population lives along our coasts.

Casco Bay Estuary Partnership: Portland Waterfront

Coastal counties are growing three times faster than counties elsewhere in the nation. Unfortunately, the increasing concentration of people and accompanied land use changes upset the natural balance of estuarine ecosystems and create additional pressure on natural resources. What happens on the land affects the quality of the water and health of all life that depend on estuaries. For example, rain or snow melt that flows over an agricultural area or an urbanized area picks up sediment, animal waste, fertilizer, pesticides, motor oil, untreated sewage from failing septic tanks, and industrial wastewater. Drop by drop, water is channeled into soils, groundwaters, creeks, and streams, making its way to larger rivers, through the estuary and eventually the sea. The total pollution impacts the quality of the water and the overall vitality and health of the entire ecosystem.