Chuuk Lagoon, also known as Truk Lagoon, is a sheltered body of water in the central Pacific. About 1800 km north-east of New Guinea, it is located mid-ocean at 7 degrees North latitude, and is part of Chuuk State within the Federated States of Micronesia. The atoll consists of a protective reef, 225 kilometres (140 mi) around, enclosing a natural harbour 79 by 50 kilometres (49 by 30 mi), with an area of 2,130 square kilometres (820 sq mi). It has a land area of 127.4 square kilometres (49.2 sq mi), with a population of 34,651 people and a maximal height of 443 m. Weno island functions as state capital and is the largest city in the FSM with its 14,000 people.
Chuuk means mountain in the Chuukese language. The lagoon was known mainly as Truk (a mispronunciation of Ruk), until 1990. Other names included Ruk, Hogoleu, Torres, Ugulat, and Lugulus.
Chuuk Lagoon is part of the larger Caroline Islands group. The area consists of eleven major islands (corresponding to the eleven municipalities of Truk lagoon, which are Tol, Udot, Fala-Beguets, Romanum, and Eot of Faichuk group, and Moen, Fefan, Dublon, Uman, Param, and Tsis of Namoneas group) and forty-six smaller ones within the lagoon, plus forty-one on the fringing coral reef, and is known today as the Chuuk islands, part of the Federated States of Micronesia in the Pacific Ocean.