Estuary

Article By:

MacDonald, Daniel G. Department of Estuarine and Ocean Science, University of Massachusetts-Dartmouth, New Bedford, Massachusetts.

Dyer, K. R. Institute of Oceanographic Sciences, Somerset, United Kingdom.

Last reviewed:June 2020

DOI:https://doi.org/10.1036/1097-8542.242800

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• Estuarine oceanography, published November 2019:Download PDF Get Adobe Acrobat Reader

A semienclosed coastal body of water which has a free connection with the sea and within which the seawater is measurably diluted by freshwater derived from land drainage. In estuaries, the seawater diluted by freshwater is called brackish water, and its salinity ranges from 0.5 to 35 parts per thousand. Many characteristic features of estuaries extend into the coastal areas beyond their mouths (Fig. 1). Semienclosed bays and lagoons also exist in which evaporation is equal to or exceeds freshwater inflow, so that the salt content either is equal to that of the sea or exceeds it. Hypersaline lagoons have been termed negative estuaries, whereas those with precipitation and river inflow equaling evaporation have been called neutral estuaries. Positive estuaries, in which river inflow and precipitation exceed evaporation, form the majority. See also: Freshwater ecosystem; Seawater

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