The Mekong is south-east Asia's longest river (around 4 900km). From its source in Tibet, it flows southwards through the Chinese province of Yunnan before passing through five south-east Asian countries (Myanmar, Thailand, Laos, Cambodia and Vietnam). Nearly half of the river is in China, where it is known as the Lancang. For the 70 million people who live in the Mekong basin, the river is a vital source of food and water, as well as an important transport route. Increasingly, it is being used to generate hydroelectricity. Human activity threatens the river's fauna and flora, and competition for natural resources is intensifying.