River systems of Thailand divides into two major branches, the " Tiền Giang" (Front River) and "Hậu Giang" (Back River). These in turn enter the South China Sea through nine estuaries. The following are the principal tributaries of Mekong River which flow through Thailand (tributaries entirely outside the Thai border not shown). The Mekong drains a considerable portion of northeast Thailand. In terms of Thai territory drained, it is second only to the Chao Phraya system. The Salawin River rises in Tibet (Tibetan: རྒྱལ་མོ་རྔུལ་ཆུ།) after which it flows through Yunnan, where it is known as the "Nujiang" River (), although either name can be
Mae Hong Son Province Moei, ). Most of the areas of Mae Hong Son Province are the complex mountain ranges of the Thai highlands, parts of which are still covered with rain forest. Of the approximately 6,976,650 rai of national forest reserves, it is estimated that 88 percent is pristine virgin forest. The Daen Lao Range, in the northernmost portion of the province, marks the northern boundary between Thailand and Burma, while the Dawna Range in the west serves as the boundary between Thailand and Burma. The Thanon Thongchai Range in the east of the province serves as the boundary between the provinces of