The River Mekong is the world's 12th-longest river. From its Himalayan source on the Tibetan plateau, it flows some 4,350km (2,703 miles) through China's Yunnan province, Burma, Laos, Thailand, Cambodia and Vietnam, finally draining in the South China Sea. The recent construction of hydroelectric dams on the river and its tributaries has reduced the water flow dramatically during the dry season in Southeast Asia. In this 1867 drawing by Louis Delaporte, two- to three-meter-wide whirlpools prevented a French Mekong expedition from navigating the river, and they had to carry their pirogues and cargo upstream.