Apo Reef is a coral reef system in the Philippines situated in the western waters of Occidental Mindoro province in the Mindoro Strait. Encompassing , it is considered the world's second-largest contiguous coral reef system, and is the largest in the country. The reef and its surrounding waters are protected areas administered as the Apo Reef Natural Park (ARNP). It is one of the best known and most popular diving regions in the country, and is in the tentative list for UNESCO World Heritage Sites. Geography Apo Reef can is about west of the nearest coast of the Philippine island of Mindoro. It is separated from main island by the Apo east Pass of the Mindoro Strait. Politically, the reef lies within the jurisdiction of the Province of Occidental Mindoro in Region IV-B of the Philippines and more specifically of the Municipality of Sablayan. Tourism activities are administered by the local government of Sablayan and the local office of the Department of Environment and Natural Resources (DENR). Reef system Apo Reef is a roughly triangular coral atoll formation approximately from the north to the south tip, and from east to west. It is separated by two lagoon systems, the north and south lagoons which are bounded by narrow reef platforms. It is of almost triangular northern and southern atoll-like reefs separated by a deep channel that is open to the west. The channel runs east to west from deep with a fine white sand bottom, numerous mounds and patches of branching corals under the deep blue water. The north lagoon is an enclosed triangular coral reef platform partly exposed during low tide. It is relatively shallow with depths of about . While the south lagoon is an inverted triangular coral platform enclosed on two sides and is about in depth. Likewise, reef limestone and coralline sand on the east and southeastern sides dominantly underlie the area. Islands The main geographical feature of Apo Reef is submerged, but three islands mark it on the surface: the Apo Island, Apo Menor (locally known as Binangaan) and Cayos del Bajo ("Keys of the bank", locally known as Tinangkapan). The islands are uninhabited. Since the declaration of "no-take-zone" policy at Apo Reef Natural Park in 2007, only protected area personnel and members of the Task Force MARLEN (Marine and Apo Reef Law Enforcement for Nature), who are tasked to implement protection and conservation work