Chuukh Lagoon, also known as Truk Lagoon, is situated at the northeast of the New Guinea and is a part of Chuukh State, Micronesia. During World War II, it served as a naval base for the Japanese. It consists of a protective reef that encloses a natural harbor 79 by 50 kilometers with the land area covering 127.4 square kilometers and is a part of the larger Caroline Islands group. It comprises of seven major islands and forty-six smaller ones lying within the lagoon and an additional forty-one lying on the coral reef. The Chuukh Lagoon has an underwater fleet that has been designated as a National Historic Landmark. It also includes a group of outer islands namely Mortlock Islands, Hall Islands, Namonuito Atoll and Pattiw. It is famous for its wreck diving.
The underwater fleet is suffering severe deterioration, looting and vandalism. The spear and line fishing have damaged the resources. Within the lagoon are the submerged remains of tankers, freighters, supply vessels and the Fumitsuk, a Japanese submarine. There are 35 sunken vessels that lie between Dublon and Fefan Islands.