Lagoon

File:BalosLagoonCreta.jpg

Balos coastal lagoon of northwestern Crete. The shallow lagoon is separated from the Mediterranean Sea by narrow shoals connecting to a small, rocky mountain.

File:Kara-Bogaz Gol from space, September 1995.jpg

Garabogazköl lagoon in Turkmenistan

File:Venice Lagoon December 9 2001.jpg

Venetian Lagoon

A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as a reef, a barrier island or islands, a barrier peninsula, or an isthmus. 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 shoal, 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.

Many lagoons do not include "lagoon" in their common names. Currituck, Albemarle and Pamlico Sounds in North Carolina, Great South Bay between Long Island and the barrier beaches of Fire Island in New York, Isle of Wight Bay, which separates Ocean City, Maryland from the rest of Worcester County, Maryland, Banana River in Florida, US, Lake Illawarra in New South Wales, Australia, Montrose Basin in Scotland, and Broad Water in Wales have all been classified as lagoons, despite their names. In England, The Fleet at Chesil Beach has also been described as a lagoon.

In some languages the word for a lagoon is simply a type of lake: In Chinese a lake is (), and a lagoon is (). In the French Mediterranean several lagoons are called étang ("lake"). Contrariwise, several other languages have specific words for such bodies of water. In Spanish, coastal lagoons generically are , but those on the Mediterranean coast are specifically called . In Russian and Ukrainian, those on the Black Sea are (), while the generic word is (). Similarly, in the Baltic, Danish has the specific , and German the specifics and Haff, as well as generic terms derived from . In Poland these lagoons are called zalew ("bay"), and in Lithuania marios ("lagoon, reservoir"). In Jutland several lagoons are known as fjord. In New Zealand the Māori word refers to a coastal lagoon formed at the mouth of a braided river where there are mixed sand and gravel beaches, while , an ephemeral coastal waterbody, is neither a true lagoon, lake, nor estuary.

Some languages differentiate between coastal and atoll lagoons. In French, refers specifically to an atoll lagoon, while coastal lagoons are described as , the generic word for a still lake or pond. In Vietnamese, refers to an atoll lagoon, whilst is coastal.

In Latin America, the term 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" (). In Portuguese, a similar usage is found: may be a body of shallow seawater, or a small freshwater lake not linked to the sea.

Etymology

Lagoon is derived from the Italian , which refers to the waters around Venice, the 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

File:Atafutrim.jpg

Satellite picture of the Atafu atoll in Tokelau in the Pacific Ocean

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 (>Template:Convert) portions.

Coastal lagoons

File:Caspian Sea covered with plants near Bandar-e Anzali - Barry Kent.jpg

Anzali Lagoon in southwestern Caspian Sea coast, Iran

File:Hiddensee (2011-05-21).JPG

Coastal lagoon landscapes around the island of Hiddensee near Stralsund, Germany. Many similar coastal lagoons can be found around the Western Pomerania Lagoon Area National Park.

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 Template:Convert. 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 Eastern and Gulf Coasts.

Coastal lagoons can be classified as leaky, restricted, or choked. 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. Mangroves and marsh plants can facilitate the accumulation of sediment in a lagoon. Benthic organisms may stabilize or destabilize sediments.

Largest coastal lagoons

Lagoon	Area	Country
New Caledonian lagoon	Template:Convert	Template:Country
Garabogazköl	Template:Convert	Template:Country
Lake Maracaibo	Template:Convert	Template:Country
Template:Efn	Template:Convert	Template:Country
Albemarle-Pamlico sound system	Template:Convert	Template:Country
Lagos Lagoon	Template:Convert	Template:Country
Curonian lagoon	Template:Convert	Template:Country /Template:Country
Mayotte lagoon	~Template:Convert	Template:Country
Rangiroa lagoon	Template:Convert	Template:Country
Chilika Lake	Template:Convert during monsoon season, Template:Convert during dry season	Template:Country
Caratasca Lagoon	Template:Convert	Template:Country
Indian River Lagoon	Template:Convert	Template:Country
Vistula lagoon	Template:Convert	Template:Country /Template:Country
Biscayne Bay System —Biscayne Bay (traditional)	Template:Convert Template:Convert	Template:Country
Marovo lagoon	Template:Convert	Template:Country
Szczecin Lagoon	Template:Convert	Template:Country / Template:Country
Venetian Lagoon	Template:Convert	Template:Country

See also

• Aerated lagoon
• Anaerobic lagoon
• Ayre (landform)
• Barachois
• Braided river
• Estuary
• Haff (estuarine lagoon)
• Longshore drift
• Sediment transport