Estuary

An estuary is a semi-enclosed coastal body of water which has a free connection with the open sea and within which sea water mixes with fresh water. The key feature of an estuary is that it is a mixing place for sea water and a significantly-sized river to supply fresh water. A tide is a necessary component to maintain a dynamic relationship between the two waters. Though something in the nature of an estuary can exist in a non-tidal sea, such areas go by names such as lagoon, étang or laguna. In non-tidal seas, the rivers naturally form deltas rather than estuaries.

An estuary is typically the tidal mouth of a river, and estuaries are often characterised by sedimentation of silt which usually comes mainly from the sea though in some cases, that from the river predominates. The sand and mud banks and marshes are relied upon as habitat, by for example, wading birds. Estuaries are more likely to occur on submerged coasts, where the sea level has risen in relation to the land, as this process floods valleys to form rias, fjords etc, which can be classified as estuaries in cases where there is a significant river flowing into them.

The estuaries are sometimes confused with fjords. The Lim bay in Istria, Croatia, is often called "Lim fjord" although it's not actually caused by glaciation but by land erosion by the river Pazinčica.

See also

• Brackish water
• List of waterways

References

• Pritchard, D. W. (1967) What is an estuary: physical viewpoint. p. 3–5 in: G. H. Lauf (ed.) Estuaries, A.A.A.S. Publ. No. 83, Washington, D.C.

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