The Mekong is the third-longest river in Asia, running an estimated 4,909 km (3,050 mi) from the Tibetan Plateau through China, Myanmar, Laos, Thailand and Cambodia to its delta in southern Vietnam, where it drains a basin of about 795,000 km² into the South China Sea. It matters because it carries one of the world’s largest inland fisheries, about two million tonnes of wild fish a year, and the delta grows more than half of Vietnam’s rice. That is also why the river’s threats, from a cascade of hydropower dams to sand mining, a sinking delta and a dwindling dolphin population, are watched so closely, and why its protections, from the 1995 Mekong Agreement to UNESCO and Ramsar listings, carry real weight for tens of millions of people.
Two Million Tonnes of Fish: What the Mekong Stands to Lose
Every threat to the Mekong is ultimately measured in fish. The lower basin lands an estimated two million tonnes of wild fish a year, plus almost 500,000 tonnes of crabs, shrimp, snakes, frogs and other aquatic animals, and aquaculture adds about two million tonnes more. The total value of the fishery is put at between US$3.9 billion and US$7 billion a year. Around 40 million rural people, more than two-thirds of the lower basin’s rural population, take part in the wild-capture fishery; in Laos 71% of rural households, about 2.9 million people, rely on it for food or cash, and more than 1.2 million people live in fishing communes around Cambodia’s Tonlé Sap lake.
For nutrition the stakes are higher still. Aquatic resources supply between 47% and 80% of the animal protein in rural diets of the lower basin, and around 80% of Cambodians’ annual protein intake comes from fish caught in the Mekong system. Much of that catch depends on migration: a WWF and UN Food and Agriculture Organization study coordinated by the WorldFish Center found 229 fish species whose spawning and migration would be affected by a mainstream dam.
Manwan to Nuozhadu: China’s Lancang Dam Cascade
The upper river, known in China as the Lancang, holds most of the mainstream dams. The Manwan Dam in Yunnan has a capacity of 1,570 MW. The largest so far, Nuozhadu, is a 261.5-metre embankment dam begun in 2004; its first generator went online on 6 September 2012 and the last in June 2014, giving it 5,850 MW of capacity and a reservoir of about 21.7 billion m³. As of February 2024, 13 of the 15 hydropower plants on the Mekong mainstream were in China, with a further mainstream dam under construction there.
These reservoirs matter downstream because the “Yunnan component” of the river, largely snowmelt from the Tibetan Plateau, still makes up almost 30% of the average dry-season flow as far south as Kratié in Cambodia, and as much as 40% in the dry season at that point by another measure. When those reservoirs store or release water, the low-flow season in Laos and Cambodia changes with them. In 2016 China launched the Lancang–Mekong Cooperation, a forum whose central purpose is to manage the release of water from its dams with the five downstream countries.
Xayaburi, Don Sahong and Lower Sesan 2: Dams Below the Golden Triangle
The lower Mekong stayed undammed on its mainstream until the 2010s. The Xayaburi Dam, about 30 km east of Sainyabuli in northern Laos, was the first of 11 dams planned on the lower river. Under the 1995 Mekong Agreement, Laos began the Mekong River Commission’s prior-consultation process in September 2010; on 19 April 2011 the commission’s joint committee announced that Cambodia, Laos, Thailand and Vietnam could not reach consensus. Laos nonetheless let the Thai developer CH. Karnchang resume work, construction formally restarted with a ceremony on 7 November 2012, and the 32.6-metre, 820-metre-long dam began commercial operation in October 2019. About 95% of its 1,285 MW goes to Thailand’s state utility, EGAT. It has a navigation lock and two fish passes, though fisheries scientists warned that no fish passage on that scale had been proven in the tropics.
The pattern repeated at the Don Sahong Dam, which blocks the Hou Sahong channel in the Siphandone (“4,000 islands”) area of southern Laos, less than 2 km above the Cambodian border. Laos notified the commission on 30 September 2013, argued that a dam on a side channel did not require prior consultation, agreed in June 2014 to go through it anyway, and again saw no consensus. The 22.5-metre, 260 MW dam was commissioned in 2020. On the Se San tributary in Cambodia’s Stung Treng province, the 400 MW Lower Sesan 2 Dam, first judged unattractive in a 1999 Asian Development Bank study, opened on 18 December 2018; up to 2,000 people were to be displaced, and its effects on fisheries were expected to reach as far as the Tonlé Sap. On 19 July 2019, in the middle of the wet season, the reach from Chiang Saen to Vientiane fell to its lowest level in a century, and locals blamed the newly built Xayaburi.
The Mekong River Commission has forecast that dam projects would reduce aquatic life in the basin by 40% by 2020 and deplete fish by 80% by 2040, with Thailand’s Mekong fish stocks falling by 55%, Laos’s by 50%, Cambodia’s by 35% and Vietnam’s by 30%.
Sand Mining, Lost Sediment and a Sinking Mekong Delta
Dams trap more than water. The Mekong still carries over 160 million tonnes of sediment a year, including about 6.5 million tonnes of sand, but historic loads were higher, and damming in the upper basin plus sand mining in the riverbed in Laos, Cambodia and Vietnam have both cut the supply. Sand dredging destabilises riverbanks, starves floodplains of silt, raises salinity and displaces species.
The result shows on the coast. Between 1973 and 2005 the seaward shoreline of the delta was still advancing, but its growth slowed from 7.8 metres a year to 2.8; after 2005 it turned to a retreat of about 1.4 metres a year, and net land gain fell from 4.3 km² a year in the 1970s to slightly negative in 2005–2015. In other words, around 2005 the delta passed from building land to losing it. The land is also sinking, by about 1.1 cm a year. A 2019 study in Nature Communications found the delta averages only 0.82 m above sea level and that 75% of it, home to 12 million people, lies below 1 m. One key road in Cần Thơ, flooded on 72 days a year, is forecast to be under water on 270 days a year by 2030. Vietnam’s Resolution 120 of 2017 emphasised nature-based solutions for the delta, such as mangrove restoration, retrofitted dikes and multi-value farming.
Forest Loss, Sewage, Plastic and Blasted Rapids
Other pressures build up across the basin. On Thailand’s Khorat Plateau, which drains through the Mun and Chi rivers, forest cover fell from 42% in 1961 to 13% in 1993; in Cambodia it fell from 73% in 1973 to 63% in 1993, and in Vietnam’s Central Highlands from over 95% in the 1950s to around 50% by the mid-1990s. Sewage treatment is rudimentary in many riverside towns, including Vientiane, and the Mekong is counted among the ten rivers that carry most of the plastic reaching the oceans. As of 2025, tin and rare-earth mining in Myanmar’s Karen and Shan states was adding pollution to the basin. Climate change is lengthening and heating the dry season, and UNICEF describes the rainy season as increasingly unpredictable.
Navigation projects brought their own risk. A 2015–2025 plan by China, Myanmar, Laos and Thailand proposed blasting rapids so 500-tonne cargo boats could sail 890 km from Yunnan to Luang Prabang. Thailand agreed “in principle” in December 2016, but on 4 February 2020 its cabinet voted to stop blasting and dredging 97 km of riverbed.
The Last Irrawaddy Dolphins of Kratié
The river’s most visible casualty is its freshwater dolphin. The Irrawaddy dolphin was once found throughout the lower Mekong; by 2024 about 105 animals survived in a 190 km stretch in Cambodia, and the species has been extinct in the Laotian Mekong since 2022. Gillnets and explosive fishing are the main threats, and the IUCN lists the Mekong subpopulation as critically endangered.
Protection has come in steps. In 2004 CITES moved the Irrawaddy dolphin to Appendix I, banning commercial trade. WWF set up the Cambodian Mekong Dolphin Conservation Project in 2005; the Kratie Declaration on the Conservation of the Mekong River Irrawaddy Dolphin was signed in January 2012; and on 24 August 2012 Cambodia declared a 180 km stretch from eastern Kratié to the Lao border a limited fishing zone, banning floating houses, fish cages and gillnets, patrolled by river guards. The river’s giant fish are in similar trouble: the Mekong giant catfish, whose 293 kg record specimen was caught in Thailand in 2005, is critically endangered, and in 2022 a 300 kg giant freshwater stingray caught in Cambodia became the largest freshwater fish on record.
From the 1957 Mekong Committee to UNESCO and Ramsar Listings
The legal framework is older than most of the dams. A United Nations commission’s report led to the Mekong Committee in September 1957. Its successor, the Mekong River Commission, was created by the Agreement on the Cooperation for the Sustainable Development of the Mekong River Basin, signed in Chiang Rai on 5 April 1995 by Cambodia, Laos, Thailand and Vietnam; China and Myanmar became dialogue partners in 1996. The agreement’s procedures for notification and prior consultation are the ones tested, and found non-binding, at Xayaburi and Don Sahong.
Protected areas now run from source to sea. The headwaters lie in the Sanjiangyuan National Nature Reserve, established in May 2000 and raised to national status in January 2003, with Sanjiangyuan National Park following in 2021. The river’s Yunnan gorges belong to the Three Parallel Rivers of Yunnan Protected Areas, a UNESCO World Heritage Site since 2003. UNESCO designated the Tonlé Sap a biosphere reserve in 1997, a 2001 royal decree created the Tonlé Sap Biosphere Reserve, and its core zones are Prek Toal, Boeng Chhmar and Stung Sen; Prek Toal is also a Ramsar site. In the delta, Tràm Chim National Park, created on 29 December 1998 in the Plain of Reeds to protect the sarus crane, is a Ramsar wetland of international importance. How well these protections hold will decide the future of the Tonlé Sap wetlands and of the Mekong Delta, and much of it turns on choices made upstream in Laos.