An atoll (pronounced /'æt?l/) is an island of coral that surrounds a lagoon partially or completely.
Distribution and size
The distribution of atolls worldwide is instructive: most of the world's atolls are located in the Pacific Ocean (with concentrations in the Tuamotu Islands, Caroline Islands, Marshall Islands, Coral Sea Islands, and the island groups of Kiribati, Tuvalu and Tokelau) and the Indian Ocean (Atolls in the Maldives, Laccadive Islands, Chagos Islands and the Outer Islands of the Seychelles). The Atlantic Ocean does not have a large group of atolls more than the eight atolls east of Nicaragua that belong to the departments of San Andres and Providencia in Colombia in the Caribbean Sea.
Coral-making corals can only live in tropical and subtropical warm oceans and seas, and previously atolls could only be found in tropical and subtropical areas. The northernmost atoll in the world is Kure Atoll at 28°24' N, along with other atolls in the Northwest Hawaiian Islands. The world's southernmost atolls are Elizabeth Reef at 29°58' S, and Middleton Reef at 29°29' S, in the Tasman Sea, both part of the Coral Sea Islands Territory. The next southernmost atoll is Ducie Island in the Pitcairn Islands, at 24°40' S. Bermuda is sometimes claimed to be the "northernmost atoll" at latitude 32°24' N. At this latitude corals cannot survive without the warm waters of the Gulf streams. However, Bermuda is referred to as a pseudo-atoll because its original form, while forming an atoll, has a very different shape. While no atoll is located directly on the Equator, the closest atoll to the Equator is Aranuka in Kiribati, with its southern end 12 km north of the Equator.
The largest atolls by area (lagoon plus coral and dry land) are (information from ):
Saya de Malha Bank, West Indian Ocean (35000 km²) (without separate North Bank), submerged, at a depth of 7 m,
Lansdowne Bank, west of New Caledonia (21000 km²), submerged, at a depth of 3.7 m 
Great Chagos Bank (12642 km², land area only 4.5 km²)
Reed Bank, Spratly Islands (8866 km²), submerged, at a depth of 9 m
Macclesfield Bank, South China Sea (6448 km²), submerged, at 9.2 m
North Bank (Ritchie Bank, north of Saya de Malha Bank (5800 km²), submerged, at depth <10 m
Cay de Sal Bank, Bahamas (5226.73 km², land area 14.87 km²)
Rosalind Bank, Caribbean Sea (4500 km²), submerged, at a depth of 7.3 m
Thiladhunmathi-Miladhunmadulu Atoll, Maldives, (two names, but one single atoll structure) (3850 km², land area 51 km²)
Chesterfield Islands, New Caledonia (3500 km², land area <10 km²)
Huvadhu Atoll, Maldives (3152 km², land area 38.5 km²)
Truck Lagoon, Chuuk (3130 km²) Archived 2011-09-27 at Wayback Machine.
Sabalana Islands, Indonesia (2694 km²)
Lihou Reef, Coral Sea (2529 km². land area 1 km²)
Bassas de Pedro (2474.33 km², submerged, at a depth of 16.4 m
Ardasier Bank, Spratly Islands (2347 km²), cay on the south side?
Kwajalein, Marshall Islands (2304 km², land area 16.4 km²)
Diamond Islets Bank, Coral Sea (2282 km², land area <1 km²)
Namonuito Atoll, Chuuk (2267 km², land area 4.4 km²)
Ari Atoll, Maldives (2252 km², land area 69 km²)
Maro Reed, Northwest Hawaiian Islands, 1934 km²
Rangiroa, Tuamotu Islands (1762 km², land area 79 km²)
Kolhumadulhu Atoll, Maldives (1617 km², land area 79 km²)
North Malé Atoll, Maldives (1565 km², land area 69 km²)
Ontong Java, Solomon Islands (1500 km², land area 12 km²) In some ways, the land area of an atoll is very small compared to its total area. According to , Lifou (1146 km² land area) is the largest surface coral atoll in the world, followed by Rennell Island (660 km²). Many sources state that the largest atoll in the world by land area is Kiritimati, which is also a surface coral atoll (321.37 km² land area; according to other sources 575 km²), the main lagoon of 16