Estuaries are important natural places. In addition to essential habitats for birds, fish, insects, and other wildlife, estuaries provide goods and services that are economically and ecologically indispensable, such as commercial fishing and recreational opportunities.
Estuaries provide critical habitat for species that are valued commercially, recreationally, and culturally. Birds, fish, amphibians, insects, and other wildlife depend on estuaries to live, feed, nest, and reproduce. Some organisms, like oysters, make estuaries their permanent home; others, like horseshoe crabs, use them to complete only part of their life cycle. Estuaries provide stopovers for migratory bird species such as mallard and canvasback ducks. Many fish, including American shad, Atlantic menhaden and striped bass, spend most of their lives in the ocean, but return to the brackish waters of estuaries to spawn.
Estuaries are often the economic centers of coastal communities. Estuaries provide habitat for more than 75 percent of the U.S. commercial fish catch, and an even greater percentage of the recreational fish catch. The total fish catch in estuaries contributes billions of dollars a year to the U.S. economy.
Estuaries are also important for other recreational activities. Millions of people visit estuaries each year to boat, swim, fish, and watch birds and other wildlife.
Many estuaries are important centers of transportation and international commerce. Many of the products you use daily pass through one or more estuaries on a commercial shipping vessel before ever reaching your home.
The continuing prosperity many coastal communities reap from fishing and tourism is clearly linked to the health of their estuaries. The economy and the environment are completely intertwined.
While strongly affected by tides and tidal cycles, many estuaries are protected from the full force of ocean waves, winds, and storms by reefs, barrier islands, or fingers of land, mud, or sand that surround them. The characteristics of each estuary depend upon the local climate, freshwater input, tidal patterns, and currents. Truly, no two estuaries are the same. Yet they are typically classified based on two characteristics: their geology and how saltwater and fresh water mix in them.
However, not all estuaries contain brackish waters. There are a small number of ecosystems classified as freshwater estuaries. These estuaries occur where massive freshwater systems, such as the Great Lakes in the United States, are diluted by river or stream waters draining from adjacent lands.