A lagoon is a shallow
body of water separated from a larger body of water by a narrow
landform, such as
barrier islands, barrier peninsulas, or
isthmuses. Lagoons are commonly divided into coastal lagoons (or barrier lagoons) and atoll lagoons. They have also been identified as occurring on mixed-sand and gravel coastlines. There is an overlap between bodies of water classified as coastal lagoons and bodies of water classified as
estuaries. Lagoons are common coastal features around many parts of the world.
Definition and terminology
Lagoons are shallow, often elongated bodies of water separated from a larger body of water by a shallow or exposed
coral reef, or similar feature. Some authorities include
fresh water bodies in the definition of "lagoon", while others explicitly restrict "lagoon" to bodies of water with some degree of
salinity. The distinction between "lagoon" and "estuary" also varies between authorities. Richard A. Davis Jr. restricts "lagoon" to bodies of water with little or no fresh water inflow, and little or no
tidal flow, and calls any
bay that receives a regular flow of fresh water an "estuary". Davis does state that the terms "lagoon" and "estuary" are "often loosely applied, even in scientific literature". Timothy M. Kusky characterizes lagoons as normally being elongated parallel to the coast, while estuaries are usually drowned river valleys, elongated perpendicular to the coast. Coastal lagoons are classified as inland bodies of water.
When used within the context of a distinctive portion of coral reef ecosystems, the term "lagoon" is synonymous with the term "back reef" or "backreef", which is more commonly used by coral reef scientists to refer to the same area.
In some languages the word for a lagoon is simply a type of lake: In Chinese a lake is hucode: zho promoted to code: zh (湖code: zho promoted to code: zh ), and a lagoon is xihucode: zho promoted to code: zh (潟湖code: zho promoted to code: zh ). Contrariwise, several other languages have specific words for such bodies of water. In Spanish, coastal lagoons generically are laguna costeracode: spa promoted to code: es , but those on the Mediterranean coast are specifically called albuferacode: spa promoted to code: es . In Russian and Ukrainian, those on the
Black Sea are limancode: rus promoted to code: ru (лиманcode: rus promoted to code: ru ), while the generic word is lagunacode: ukr promoted to code: uk (Лагунаcode: ukr promoted to code: uk ). Similarly, in the
Baltic, Danish has the specific Nor [
da], and German the specifics Boddencode: deu promoted to code: de and Haff [
de]code: deu promoted to code: de , as well as generic terms derived from lagunacode: deu promoted to code: de . In
New Zealand the
Māori word hapuacode: mri promoted to code: mi refers to a coastal lagoon formed at the mouth of a
braided river where there are mixed sand and gravel beaches, while waitunacode: mri promoted to code: mi , an
ephemeral coastal waterbody, is neither a true lagoon, lake nor estuary.
Some languages differentiate between coastal and atoll lagoons. In French, lagoncode: fra promoted to code: fr refers specifically to an atoll lagoon, while coastal lagoons are described as étang [
fr]code: fra promoted to code: fr , the generic word for a still lake or pond.
In Vietnamese, Đầm san hôcode: vie promoted to code: vi refers to an atoll lagoon, whilst Đầm phácode: vie promoted to code: vi is coastal.
In Latin America, the term lagunacode: spa promoted to code: es in Spanish, which lagoon translates to, may be used for a small fresh water
lake in a similar way a
creek is considered a small river. However, sometimes it is popularly used to describe a full-sized
lake, such as
Laguna Catemaco in Mexico, which is actually the third-largest lake by area in the country. The
brackish water lagoon may be thus explicitly identified as a "coastal lagoon" (laguna costeracode: spa promoted to code: es ). In Portuguese, a similar usage is found: lagoacode: por promoted to code: pt may be a body of shallow seawater, or a small freshwater lake not linked to the sea.
Lagoon is derived from the
Italianlagunacode: ita promoted to code: it , which refers to the waters around
Venetian Lagoon. Laguna is attested in English by at least 1612, and had been
Anglicized to "lagune" by 1673. In 1697
William Dampier referred to a "Lagune or Lake of Salt water" on the coast of Mexico.
Captain James Cook described an island "of Oval form with a Lagoon in the middle" in 1769.
Atoll lagoons form as coral reefs grow upwards while the islands that the reefs surround subside, until eventually only the reefs remain above sea level. Unlike the lagoons that form shoreward of fringing reefs, atoll lagoons often contain some deep (>20 m (66 ft)) portions.
Coastal lagoons form along gently sloping coasts where barrier islands or reefs can develop offshore, and the sea-level is rising relative to the land along the shore (either because of an intrinsic rise in sea-level, or
subsidence of the land along the coast). Coastal lagoons do not form along steep or rocky coasts, or if the range of tides is more than 4 metres (13 ft). Due to the gentle slope of the coast, coastal lagoons are shallow. A relative drop in sea level may leave a lagoon largely dry, while a rise in sea level may let the sea breach or destroy barrier islands, and leave reefs too deep underwater to protect the lagoon. Coastal lagoons are young and dynamic, and may be short-lived in geological terms. Coastal lagoons are common, occurring along nearly 15 percent of the world's shorelines. In the United States, lagoons are found along more than 75 percent of the
Coastal lagoons are usually connected to the open ocean by
inlets between barrier islands. The number and size of the inlets, precipitation, evaporation, and inflow of fresh water all affect the nature of the lagoon. Lagoons with little or no interchange with the open ocean, little or no inflow of fresh water, and high evaporation rates, such as
Lake St. Lucia, in
South Africa, may become highly saline. Lagoons with no connection to the open ocean and significant inflow of fresh water, such as the
Lake Worth Lagoon in Florida in the middle of the 19th century, may be entirely fresh. On the other hand, lagoons with many wide inlets, such as the
Wadden Sea, have strong tidal currents and mixing. Coastal lagoons tend to accumulate sediments from inflowing rivers, from runoff from the shores of the lagoon, and from sediment carried into the lagoon through inlets by the tide. Large quantities of sediment may be occasionally be deposited in a lagoon when storm waves overwash barrier islands.
marsh plants can facilitate the accumulation of sediment in a lagoon.
Benthic organisms may stabilize or destabilize sediments.
European Union, coastal lagoon habitat is classified and under Directive 92/43/EEC on the conservation of natural habitats and wild flora and fauna (
Habitats Directive). Furthermore, numerous bird species breed in coastal lagoons. As a result, many lagoons are also protected under Directive 2009/147/EC on the conservation of birds (
^Kirk, R.M. and Lauder, G.A (2000). Significant coastal lagoon systems in the South Island, New Zealand: coastal processes and lagoon mouth closure. Wellington, N.Z.:
Department of Conservation.
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^"Lagoon". Oxford English Dictionary. Vol. I A-O (Compact ed.). Oxford, England: Oxford University Press. 1971. p. 1560.