The Mekong
The Mekong is the great river of Southeast Asia. It flows for around 4,350 km from the Tibetan Plateau in China through six countries to the South China Sea. Around 60 million people depend on the Mekong for fish, water and farmland. The river also has one of the most extraordinary annual events on Earth, when an entire lake in Cambodia reverses direction and flows backwards.
- Lengthapprox. 4,350 kmTwelfth longest river in the world
- Countries6China, Myanmar, Laos, Thailand, Cambodia, Vietnam
- SourceTibetan PlateauHigh in western China
- MouthSouth China SeaThrough a vast delta in southern Vietnam
- Fish speciesapprox. 1,300Second only to the Amazon
- Unique featureTonle SapA lake that reverses direction each year
The Mekong compared to other great Asian rivers
The Mekong is the longest river in Southeast Asia and one of the most important rivers in the world for fish production. Only the Amazon has more freshwater fish species.
What is the Mekong?
The Mekong starts as glacial meltwater high on the Tibetan Plateau in China. It flows southeast through deep gorges, then forms the borders between Laos and several of its neighbours, before crossing Cambodia and emptying into the South China Sea through a delta in southern Vietnam. The river is the longest in Southeast Asia and the heart of the region's farming and fishing.
The Tonle Sap and the river that flows backwards
One of the most remarkable features of the Mekong is the Tonle Sap river and lake in Cambodia. For most of the year, the Tonle Sap river flows out of the lake and into the Mekong. But during the wet season from June to October, the Mekong rises so much that the smaller river is pushed backwards. Water floods upstream into the lake, making the Tonle Sap lake expand to roughly five times its dry-season size. This flood pulse creates one of the most productive fisheries on Earth and provides up to 70% of the protein eaten by the people of Cambodia.
Dams and disputes
China has built a series of large dams on the upper Mekong (which they call the Lancang). Many more dams are planned or under construction in Laos. The dams generate hydroelectricity and control flooding, but they hold back the silt and the flood pulse that the lower Mekong depends on. Cambodia and Vietnam, which sit downstream, have complained that the upstream dams are starving their farmlands of silt and reducing the dry-season flow.
The flood pulse on which the Tonle Sap fishery depends has been weakening in recent years, partly because of the dams and partly because of climate change. Many millions of people's livelihoods are at stake.
The Mekong Delta
The Mekong empties into the South China Sea through a vast green delta in southern Vietnam. The delta is one of the most fertile areas in Asia, producing huge amounts of rice (Vietnam is the third-largest rice exporter in the world thanks largely to the Mekong Delta). About 17 million people live in the delta, mostly on small farms growing rice, fruit and fish.
Deeper dive: the upper Mekong, dam diplomacy and saltwater intrusion
The upper 2,000 km of the Mekong, in China, runs through deep and remote gorges of the Tibetan Plateau and Yunnan Province. In China this stretch is called the Lancang Jiang ("Turbulent River"). The river drops sharply (around 4,500 metres over its length) which is why it is so attractive for hydroelectric development. China has built at least 11 large dams on the Lancang since the 1990s, with a combined capacity of around 21 gigawatts. Laos has built or is building over 70 dams on the lower Mekong and its tributaries. Together, these dams have transformed the once-wild river into a series of managed reservoirs and trapped much of the sediment that used to flow downstream.
The Mekong River Commission (MRC), established in 1995, is the main forum where the four lower Mekong countries (Laos, Thailand, Cambodia and Vietnam) coordinate on the river. China and Myanmar are not full members but participate as observers. Cooperation has been difficult: China is by far the most powerful actor and has been reluctant to share full data on its upstream dams and water releases. The Lancang-Mekong Cooperation framework, founded by China in 2016, is a parallel mechanism that some critics see as undermining the MRC.
The Mekong Delta in Vietnam is now suffering from saltwater intrusion. With the dams upstream holding back fresh water during the dry season, the river's flow at the mouth is weakening. Tides push seawater further inland, salting the rice paddies and contaminating drinking water. Climate change adds to the problem: sea levels are rising at the same time that the delta is sinking (because heavy groundwater pumping for farming is making the land subside). The Mekong Delta is one of the regions in the world most at risk from climate change, and the loss of even a fraction of its rice production would have major consequences for Asia's food supply.
The country with the most of the lower Mekong is Vietnam. China's other great river is the Yangtze.