Life in an estuary

Estuaries are areas of water and shoreline where rivers meet the ocean or another large body of water, such as one of the Great Lakes. Organisms that live in estuaries must be adapted to these dynamic environments, where there are variations in water chemistry including salinity, as well as physical changes like the rise and fall of tides. Despite these challenges, estuaries are also very productive ecosystems. They receive nutrients from both bodies of water and can support a variety of life. Because of their access to food, water, and shipping routes, people often live near estuaries and can impact the health of the ecosystem.

A great blue heron swallowing a fish while standing in still water surrounded by aquatic plants.

Great Blue Heron eating a fish in an estuary. (Image credit: NOAA News)

What are estuaries?

Many different types of plant and animal communities call estuaries home because their waters are typically brackish — a mixture of fresh water draining from the land and salty seawater. This unique combination of salty and fresh water creates a variety of habitats. Some common estuarine habitats are oyster reefs, kelp forests, rocky and soft shorelines, submerged aquatic vegetation, coastal marshes, mangroves, deepwater swamps, and riparian forests. With so many places to live and so many niches to fill it is no wonder why estuaries are some of the most productive ecosystems in the world.

Importance of estuaries

Estuaries are very important to the lives of many animal species. They are often called the “nurseries of the sea” because numerous animal species rely on estuaries for nesting and breeding. Most of the fish and shellfish eaten in the United States, including salmon, herring, and oysters, complete at least part of their life cycles in estuaries. Besides being a source for food, humans also rely on estuaries for recreation, jobs, and even our homes. A majority of the world’s largest cities are located on estuaries. This can be both a good and a bad thing. Estuaries filter out sediments and pollutants from rivers and streams before they flow into the ocean, providing cleaner waters for humans and marine life. However, coastal development, introduction of invasive species, overfishing, dams, and global climate change have led to a decline in the health of estuaries.

Estuary stewardship

Ensuring the health of our estuaries is vital to the survival of the plant and animal communities that call them home and the humans that depend on them for their way of life. To preserve our estuaries, the National Estuarine Research Reserve System was established to protect more than 1.3 million acres of estuarine habitat for long-term research, monitoring, education, and stewardship throughout the coastal United States. However, you can also help protect estuaries at your home by planting native plants, using fertilizers sparingly, and cleaning up after your pets.


Education also plays an important role in protecting our estuaries. An estuarine literate person understands the interconnectedness and interdependency of estuarine systems with other earth system in both time and space, can communicate about estuaries in a meaningful way, and is able to make scientifically informed and responsible decisions regarding estuaries and coastal areas. To create an estuarine literate society, the National Estuarine Research Reserve System has developed six estuarine principles and concepts. Educators can use this framework to build lessons and curricula that will teach their students the importance of estuaries and what they can do to help protect them.