Island County Estuaries

What is an estuary?

Grasser's Lagoon

Photo by Kathy Floyd, © 2004

An estuary is a partially enclosed body of water formed where freshwater from rivers and streams flows into the Sound where it mixes with salty sea water. In estuaries, the fresh river water is blocked from flowing freely into the open ocean by either surrounding mainland, peninsulas, barrier islands, or fringing salt marshes. This mixing of fresh and salt water creates a unique environment that brims with life of all kinds. It is a transition zone between the land and sea.

Many different habitat types are found in and around estuaries, including shallow open waters, freshwater and salt marshes, sandy beaches, mud and sand flats, rocky shores, oyster reefs, mangrove forests, river deltas, tidal pools, sea grass and kelp beds, and wooded swamps. The defining feature of an estuary is the mixing of fresh and salt water, not its geographic name. Well known estuaries include Puget Sound, San Francisco Bay, Chesapeake Bay, Boston Harbor, and Tampa Bay.

Deer Lagoon

Photo by Kathy Floyd, © 2004

Why are estuaries important?

Estuaries are critical for the survival of many species. Tens of thousands of birds, mammals, fish, and other wildlife depend on estuarine habitats as places to live, feed, and reproduce.

Estuaries provide ideal spots for migratory birds to rest and refuel during their journeys. And many species of fish and shellfish rely on the sheltered waters of estuaries as protected places to spawn, giving estuaries the nickname "nurseries of the sea." Hundreds of marine organisms, including most commercially valuable fish species, depend on estuaries at some point during their development.

Besides serving as important habitat for wildlife, the wetlands that fringe many estuaries also perform other valuable services. Water draining from the uplands carries sediments, nutrients, and other pollutants. As the water flows through fresh and salt marshes, much of the sediments and pollutants are filtered out. This filtration process creates cleaner and clearer water, which benefits both people and marine life. Wetland plants and soils also act as a natural buffer between the land and ocean, absorbing flood waters and dissipating storm surges. This protects upland organisms as well as valuable real estate from storm and flood damage. Salt marsh grasses and other estuarine plants also help prevent erosion and stabilize the shoreline.

What happens when estuaries aren't protected?

When estuary habitats are paved over, polluted by runoff, or lost to coastal land subsidence, it cripples an estuary's ability to support life. When a salt marsh is filled, it can no longer filter sediments and pollution from run off. When pollution destroys eel grass beds, young fish and shellfish can no longer hide and feed in its shelter.

Why does this matter?

To learn what Island County Beach Watchers are doing to study and help protect our estuaries, look at our Seining Project web pages.

Source: U.S. Environmental Protection Agency: National Estuary Program

The Estuary pages were researched and created by the Beach Watchers Class of 2004

More about estuaries