The Mekong or Mekong River is a trans-boundary river in East Asia and Southeast Asia. It is the world's twelfth-longest river and the third-longest in Asia with an estimated length of 4,909 km and a drainage area of 795,000 km2 , discharging 475 km3 of water annually.
From its headwaters in the Tibetan Plateau, the river runs through Southwest China , Myanmar, Laos, Thail Cambodia, and southern 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 Tibet and Southeast Asia. The construction of hydroelectric dams along the Mekong in recent decades causes serious problems for the river's ecosystem, including the exacerbation of drought.