Estuaries encompass broad ecosystems that usually extend many miles beyond the open waters of a bay or lagoon to encompass surrounding
wetlands, rivers and streams. Anything that happens on land within this sprawling watershed has a direct impact on the estuary itself. Estuaries are tidally-influenced ecological systems where rivers, streams and brooks meet the sea and fresh water mixes with salt water. These areas of transition between the sea and the land are tidally driven, like the sea, but sheltered from the full force of ocean wind and waves, more like rivers. Estuaries are generally enclosed in part by the coastline, marshes and wetlands; while the seaward border may barrier islands, coral reefs and sand or mud flats.

Every estuary is unique; each individual ecosystem has different components that complete the estuarine habitat. One estuary may be enclosed by marshes and barrier islands, while another estuary's borders are the coastline and reefs. Bodies of water that may be estuaries are: sloughs, bays, harbors, sounds, inlets and bayous.

Thousands and thousands of marine birds, mammals, fish and other forms of wildlife depend on estuaries as nurseries, feeding grounds and shelter. Estuaries also act as filters for water flowing into them from rivers, streams and brooks resulting in cleaner and clearer water along coastlines. In addition the porous, resilient salt marsh soils and grasses typically found in many estuaries absorb flood waters and dissipate storm surges. Salt marsh dominated estuaries provide natural buffers between the land and the ocean and not only protect animals and fish living in them but nearby human communities and property.

The primary threats to estuaries are linked to the rivers, streams and brooks that flow into them. Any pollutants that are in these incoming water system end of being deposited in and passing through the estuarine waters. Because of the vast amounts of watershed land that surround most estuaries, the problem of  protecting them is a difficult one. Compounding this of course are more direct threats such as ship
wastes, and pollution from factories, homes and other sources located directly on the shores of estuaries.

ANEP: Association of National Estuary Programs
The Association of National Estuary Programs (ANEP) is a non-profit organization established in 1987 dedicated to promoting responsible stewardship and a common vision for the preservation and restoration of our nation’s bays and estuaries.

Coastal America
U.S. Government Site focusing on coastal waters, including estuaries

Estuarine Research Federation
The Federation's mission is to advance understanding and wise stewardship of estuarine and coastal ecosystems worldwide.

NOAA Coastal Services Center
The NOAA Coastal Service Center us an office within the National Oceanic and Atmospheric Administration devoted to serving the nation's state and local coastal resource management programs.

The National Estuarine Research Reserve System
The National Estuarine Research Reserve System is a network of protected areas established for long-term research, education and stewardship. This partnership program between NOAA and the coastal states protects more than one million acres of estuarine land and water.

U.S. Environmental Protection Agency: Oceans, Coasts & Estuaries
Official EPS site