What Is A Lagoon? How Many Types Are There?

The Blue Lagoon and Cominotto island.

What Is A Lagoon?

When barrier islands or reefs separate a shallow body of water from a larger body of water a lagoon is formed. Lagoons are divided into two types and they are atoll lagoons and coastal lagoons. However, lagoons can occur on gravel coastlines and mixed sand. Coastal lagoons tend to be confused for water bodies known as estuaries. Lagoons are a common feature found in many coastal regions around the world. There are also artificial or the human-made lagoons which are used for the treatment of wastewater. Examples of human-made lagoons include anaerobic lagoons and aerated lagoons.

The Different Types Lagoons

Most if not all lagoons do not include the term ‘lagoon’ in their names. Common examples of water bodies around the world that are categorized as lagoons regardless of their names include the Great South Bay which is located between the barricade beaches of Fire Island in New York and Long Island. The Pamlico and Albemarle Sound located in North Carolina. The Isle of Wight Bay which divides Ocean City located in Maryland from the entire Worcester County, Maryland. Broad waters located in Wales, Banana River located in Florida, Montrose Basin Located in Scotland, and Lake Illawwarra located in New South Wales.

Atoll Lagoons

Atoll lagoons are formed when coral reefs grow upward whereas the island surrounded by the reefs deteriorates to a point where the reefs are the only feature that stands above sea level. Unlike other lagoons that form contoured reefs towards the shore, atoll lagoons usually comprise of portions which are greater than 20 meters in depth.

Coastal Lagoons

Coastal lagoons are formed in the preceding gentle coastal slopes where reefs or blockade islands can flourish away from the shoreline while the sea level rise parallel to the land along the shore. Coastal lagoons do not form along rugged coasts, hilly coastal areas or if the tidal range exceeds four meters. Since these types of lagoons require a gentle slope, coastal lagoons are often not deep. Coastal lagoons are usually affected by the variance in sea level caused by global warming. Rise in sea level can potentially destroy or breach the barrier island thus leaving the reefs deep under water to a point where they are not able to protect the lagoon. Similarly, the significant drop in sea level can leave the lagoon extensively dry. Geologically, coastal lagoons are juvenile and productive, but they have a considerably short life span. Coastal lagoons are the most common as they are found in 15% of the shorelines around the world. Coastal lagoons are largely concentrated in the United States since more than 75% of the Gulf and eastern coast shores comprise of lagoons. Lagoons that have high rates of evaporation, little to no intersection with open sea or fresh water inlet such as South Africa’s, Lake St. Lucia are highly saline whereas lagoons that do not have any interchange with high seas or fresh water such as Lake Worth Lagoon Located in Florida may be entirely fresh.

River-mouth Lagoons

River-mouth lagoons usually found on mixed sand and gravel beaches on the river coast network that a typically channeled but wandering river merges with coastal environment that is relatively altered by drift along the shoreline. River-mouth lagoons are commonly found on the South Island’s east coast region of New Zealand. River-mouth lagoons have long been identified as Hapua by the Mauri people and are usually found in the coastal paraglacial regions where population density and coastal development is minimal. Examples of Hapuas in New Zealand include Hurunui, Ashburton, and Rakaia river-mouth lagoons.

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