The Mekong River is the longest river in Southeast Asia. The river has a length of approximately 4,900 km, flowing from its source on the Tibetan Plateau in China through Myanmar, Lao PDR, Thailand, Cambodia and Viet Nam via a large delta into the sea. The river basin drains a total land area of 795,000 km2 and has a mean annual discharge of 475 km3, the tenth largest in the world.
The Mekong River Basin includes seven broad regions with diverse topography, drainage patterns and geomorphology. The basin is commonly divided into the Upper and Lower Mekong River Basin. The Upper Mekong River Basin comprises the Tibetan Plateau, the Three Rivers Area and Lancang Basin in China and Myanmar. The Lower Mekong River Basin is made up of the Northern Highlands, the Khorat Plateau, the Tonle Sap Basin and the Mekong Delta. It covers Thailand, Lao PDR, Cambodia and Viet Nam.