The Mekong is one of the world's major rivers. It is regarded as the 10th-longest river in the world, and the 10th-largest by volume (discharging 475 km³ of water annually). Its estimated length is 4880 kilometres, and it drains an area of 810,000 km². From the Tibetan Plateau it runs through China's Yunnan province, Myanmar, Thailand, Laos, Cambodia and Vietnam. All except China and Myanmar belong to the Mekong River Commission. The extreme seasonal variations in flow and the presence of rapids and waterfalls have made navigation extremely difficult.