4,350 km long, the Mekong is the world's 12th-longest river. It rises in the Tibetan Plateau, runs through China's Yunnan province, Myanmar, Laos, Thailand, Cambodia and Vietnam, before disgorging into the South China Sea.
As far as Thailand is concerned it is its largest river, and in many ways, its most important, for it forms the international boarder between parts of Laos and Cambodia.