The environments created by estuaries are extremely productive and generate more organic material than equally sized grassland, forest or agricultural areas. Unique communities of animals and plants are supported by the sheltered tidal waters of estuaries. An estuary is a partially enclosed coastal body of water that is a point of transition between saltwater and freshwater, and between land and sea.
Because of their biological productivity, estuaries provide an ideal location for migratory birds to rest and feed during their journeys. Many species of wildlife and fish rely upon the shelter of estuaries as protected spawning areas. Human infrastructure also benefits from the presence of estuaries in the form of sheltered ports and harbors that enable improved shipping and transportation. Many of the pollutants and sediments coming from upland rivers and streams flow through estuaries where they are filtered out, creating cleaner water and benefiting both human and marine life. The soils and plant life found in estuaries also form a natural buffer zone between sea and land, and help to absorb the impact of storm surges and flood waters.
Estuaries are dynamic ecosystems through which saltwater from the sea enters with the rise and fall of the tides. This saline water is diluted by the freshwater entering from upland rivers and streams. The combination of inflowing waters enables an estuary to contain a high level of nutrients in both the sediment and the water column, and creates a unique and highly supportive environment for a wide variety of plant and animal life.