Estuary: Definition, Facts, Characteristics & Examples

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  • 0:00 What Is an Estuary?
  • 0:42 The Estaurine Environment
  • 2:25 Lake Estuaries
  • 2:59 Examples of Estuaries
  • 3:45 Estuaries at Risk
  • 4:42 Lesson Summary
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Lesson Transcript
Instructor: Mary Ellen Ellis
Have you ever gone swimming, kayaking, or exploring in a marshy coastal area? If so, you were enjoying the natural beauty of an estuary, a place where rivers meet large bodies of water. These unique ecosystems are important, but also under threat.

What Is an Estuary?

An estuary is a body of water along a coast or beach that is partially enclosed by land and open to the ocean or a large lake. Estuaries occur where rivers and streams meet each other, lakes, and/or the ocean. The freshwater of rivers and streams mix with the salt water of the ocean to create brackish water; it's like a transitional ecosystem from river to sea! Like the ocean beyond, a coastal estuary is influenced by tides and weather, but it's also largely protected from the waves, storms, and strong winds that the rest of the coast experiences.

The Estuarine Environment

Estuaries are unique ecosystems unlike any other on Earth. Because the rivers forming estuaries deposit eroded materials and estuaries can host a mix of freshwater and salt water flowing in from the ocean, these ecosystems are among the most productive on Earth. This means they create more organic material than most other types of environments. All of this organic matter creates a nutrient-rich ecosystem that animals rely on for food.

The uniquely sheltered environment of an estuary is also important to the diversity of the ecosystem. Estuaries provide a safe place to live, a breeding ground, and a safe rest stop for migrating animals, along with the food needed to survive. The result is a rich, diverse, and important place for a variety of animals and plants.

For us humans, estuaries are valuable natural resources. Besides the abundance of natural beauty and the opportunity to spot wildlife, estuaries provide other, more tangible resources. Estuaries are important as recreational and scientific study sites. They also often serve as ports and harbors for cities and are the sites of abundant fisheries.

From an environmental perspective, estuaries are important to humans, animals, and plants because they provide a filtering service. As water comes down toward an estuary from uplands, it moves through wetlands, marshes, and swamps, where pollutants and sediments are removed. This results in cleaner water, which is important to the animals and plants living in estuaries and to us humans making use of the resources they provide. Estuaries also protect us from storms by providing a barrier between storm surges and infrastructure.

Lake Estuaries

Not all estuaries are along ocean coastlines, and not all involve brackish water. Rivers that empty into large freshwater bodies, like the Great Lakes, produce a special kind of estuary. These don't get the mix of salt water and freshwater that make ocean estuaries so unique, but there are chemical and physical differences between rivers and lakes that make up freshwater estuaries. These types of estuaries play ecological roles similar to that of salt water estuaries, like filtering water and playing host to fish and bird nurseries.

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