The mainland is divided in length by a central mountain range whose highest peak are Mont Panié (1,629 metres (5,344 ft)) in the north and Mont Humboldt (1,618 metres (5,308 ft)) in the southeast.The east coast is covered by a lush vegetation.The west coast, with its large savannahs and plains suitable for farming, is a drier area. Many ore-rich massifs are found along this coast.
The Diahot River is the longest river of New Caledonia, flowing for some 100 kilometres (62 mi). It has a catchment area of 620 square kilometres (240 sq mi) and opens north-westward into the Baie d'Harcourt, flowing towards the northern point of the island along the western escarpment of the Mount Panié.
Most of the island is covered by wet evergreen forests, while savannahs dominate the lower elevations. The New Caledonian lagoon, with a total area of 24,000 square kilometres (9,300 sq mi) is one of the largest lagoons in the world. It is surrounded by the New Caledonia Barrier Reef.