Cambodia is 181,035 km ², one of the smallest countries of Southeast Asia and is almost circular. In the north, Cambodia borders Thailand and Laos, Thailand in the west and to the east, Vietnam. The Gulf of Thailand lies south of Cambodia. Cambodia is 70% covered with forests and jungle. 5% of the country consists of rivers and lakes. The Mekong River and Tonle Sap Lake are the main natural features. The most important region is the central plateau, which the Mekong has made very fertile. Thousands of years ago this plain would have been a huge bay in the Pacific ocean. The Mekong has gradually filled this bay with sediment, creating a fertile plain, with large rivers and their tributaries flowing through it.