is a trans-boundary river in Southeast Asia. It is the world's twelfth longest river and the seventh longest in Asia. Its estimated length is 4,350 km (2,703 mi), and it drains an area of 795,000 km2
(307,000 sq mi), discharging 475 km3
(114 cu mi) of water annually.
From the Tibetan Plateau the river runs through China, Myanmar, Laos, Thailand, Cambodia, and Vietnam. The extreme seasonal variations in flow and the presence of rapids and waterfalls in the Mekong make navigation difficult. Even so, the river is a major trade route between western China and Southeast Asia.