The atoll of Maratua in the Derawan Archipelago off the East Kalimantan of Borneo, is a tropical atoll partially encircling a massive lagoon on one end and fringed with sheer rocky walls and coral reefs along the other end.
A series of raised coral islands make up the northern half of the atoll; the southern end is defined by a continuous ring of submerged reefs. This giant upside down U-shaped atoll covers about 384 square kilometers of sandy white beaches and mangrove forests and 3,735 square kilometers of territorial waters which contain the third highest level of marine biodiversity in the world after Raja Ampat and the Solomon Islands. The reef is covered with soft and stony coral, with the channel being the main attraction. The islands of Maratua, Sangalaki, Kakaban and Derawan — making up the Derawan Archipelago — have a reputation for offering some rather unique experiences. Prolific pelagic and reef fish including thresher shark, barracuda, snapper, dogtooth tuna, spanish mackerel, jacks, surgeonfish, scalloped hammerhead, nurse, grey reef and white tip reef sharks, manta rays and eagle rays can be found in this area. The reefs are also home to an incredible variety of soft and hard corals, some of which are very rare, and many crustaceans of all sizes such as the giant clam. The total area of the atoll is huge and, with only a small population of fisherman living in five villages scattered around the atoll, the marine environment here is still in amazing condition.