16 Jun 2009: Report

The Damming of the Mekong:
Major Blow to an Epic River

The Mekong has long flowed freely, supporting one of the world’s great inland fisheries. But China is now building a series of dams on the 2,800-mile river that will restrict its natural flow and threaten the sustenance of tens of millions of Southeast Asians.

by fred pearce

The Swift Boats are long gone. The Mekong delta is peaceful now. Vinh Long, where Americans fought skirmishes with the Vietcong, is now a holiday resort. The Westerners heading off into the remoter regions of the enormous delta point nothing more threatening than a camera — and the only ambush they face is at the hands of traders at the nearby Can Tho floating market.

Vietnam is now a fast-growing, Westernizing economy. But, paradoxically, peace and prosperity is currently the biggest threat to what is one of the world’s last great wild rivers. Almost half a century of wars in southeast Asia kept engineers away from the Mekong. Their plans for giant hydroelectric dams on the river gathered dust. But all that is changing. And on the delta, they have reason to fear the consequences, for the tens of millions of people who rely on the river’s wildness for their supper could soon see their main source of protein dry up.

Last October, Chinese engineers finished construction of the Xiaowan dam on the upper reaches of the River Mekong, in the remote southern province
International Rivers
Completed last year, China's Xiaowan dam will for the first time catch the great Mekong flood that rushes out of the Himalayan mountains.
of Yunnan. The 958-foot Xiaowan dam is the world’s tallest, as high as the Eiffel Tower. Starting this summer, the hydroelectric dam will for the first time catch the great Mekong flood that rushes out of the Himalayan mountains, and then gathers monsoon rains and snowmelt as it surges through the steep gorges of Yunnan. The reservoir will eventually be 105 miles long. The first electricity will be generated next year and help keep the lights on as far away as Shanghai, more than 1,200 miles to the east.

As China rushes to industrialize, a total of eight hydroelectric dams are planned on the Mekong. By 2014, engineers will have completed the Nuozhadu dam, which will be less high but will have an even larger reservoir. The Mekong is destined to become China’s new water tower and electrical powerhouse.

This cascade of dams will be able to store half the entire flow of the Mekong as it leaves China and rushes downstream toward Burma, Thailand, Laos, Cambodia, and Vietnam. In the future, the annual flood will be released gradually as turbines are switched on and off to supply year-round electricity. From then on, the river will rise and fall at the whim of engineers rather than nature.

In late May, a report from the United Nations Environment Programme
The dams will largely eliminate the Mekong's annual flood pulse, one of the natural wonders of the world.
warned that these dams are “the single greatest threat” to the future of the river and its fecundity. The new regime will largely eliminate the river’s annual flood pulse, one of the natural wonders of the world, and wreck the ecosystems that depend on it.

Aviva Imhof, campaigns director at the International Rivers Network, said that the dams will cause incalculable damage downstream. “China is acting at the height of irresponsibility,” said Imhof. “Its dams will wreak havoc with the Mekong ecosystem as far downstream as the Tonle Sap. They could sound the death knell for fisheries which provide food for over 60 million people.”

Experts in downstream countries have been reluctant to criticize China’s policies. But Professor Ngo Dinh Tuan from Hanoi Water Resources University told Vietnamese reporters last month, “If China builds dams to serve power production, the first impact would be a remarkable reduction of aquatic resources. It would be very dangerous for people who live in the lower section.”

Until now, the waters of the Mekong have been a natural resource for humans and nature alike — on a par with the Amazon rainforest. The 2,800-mile river sustains the world’s second-largest inland fishery, a mainstay of the region’s economy for millennia. It makes the Cambodians, who are among the world’s poorest people, among the best fed. It is a direct result of the intensity of the river’s summer flood, and in particular of one feature of the flood — the river that runs backwards.

That river is the Tonle Sap, a tributary of the Mekong in Cambodia that is the beating heart of the Mekong River system. But according to the author of the UN report, Mukand Babel of the Asian Institute of Technology in Bangkok, Thailand, it is among the river system’s most vulnerable elements. China’s dams could still the beating heart.

For seven months of the year, the Tonle Sap flows from a lake in the center of Cambodia and joins the main river in front of the royal palace in Cambodia’s capital city, Phnom Penh. But each June, that downhill flow halts, and for five months — until November — the river reverses. This happens because the summer floods increase the Mekong’s flow 50-fold. So much water comes coursing down the Mekong that the river’s main channel cannot contain it.

The water has to go somewhere, and it backs up into the Tonle Sap. The tributary flows back upstream for some 125 miles into its lake, which expands hugely, flooding surrounding forests. At the height of the monsoon season, this reverse flow swallows a fifth of the Mekong’s raging waters, making the tiny Tonle Sap for a while one of the world’s biggest rivers, albeit flowing backwards.

During this flood, the submerged forest around the lake becomes the nursery for the Mekong fishery. In the silty water among the tree roots, billions of fish fry grow into fat adults. The flooded forest of the Tonle Sap
The Mekong is a reminder of how the world’s rivers used to be before the dam-builders got to work.
is one of the most productive ecosystems on Earth. And each November, as the Mekong flood abates, the Tonle Sap turns, the lake empties, and the fish swim out. To mark this annual event, Cambodia has held a huge water festival in Phnom Penh since the 12th century. Over the ensuing months, the fish will migrate for hundreds of miles up and down the Mekong — filling nets that feed tens of millions of people. Two-thirds of the fish in the Mekong begin their life in the Tonle Sap.

The most extraordinary product of this fishery is the giant catfish. The protected species grows up to three meters long and can weigh a third of a ton. Its numbers are declining, but it still lurks in huge hollowed-out pools on the river bed, some of them 400 feet deep, and occasionally turns up in the nets that fishermen put across the Tonle Sap.

This riverine cornucopia happens under the eye of the great temples of Angkor Wat. These remains of an ancient civilization that prospered here a thousand years ago sit on the lake’s north shore, on the fringe of the flooded forest. It was the Mekong fishery, centered on the lake, that sustained this empire.

The Mekong is a reminder of how the world’s rivers used to be before the dam-builders got to work. Two-thirds of our rivers today, including most of the largest, have dams holding back their natural flood pulses on their main channels. China has already dammed the other major Asian rivers that flow out of Tibet, including the Yellow River and the Yangtze, which is now stopped by the Three Gorges Dam.

They are tamed, but much less productive as a result. The Mekong is the exception. No river on Earth has such variation in flow. Only the Amazon has greater biodiversity. Only the Amazon produces more fish.

There is scarcely a mile of riverbank along the Mekong where nobody is taking fish. And yet the fishery keeps providing. Some 60 million people eat or draw their income directly from the river. They include three-quarters of the population of Cambodia where, according to Oxfam, “river fisheries make a bigger contribution to economic well-being and food security than in any other country.”

The precise effect of China’s dams will depend on how they are operated. But according to operating instructions seen by Western hydrologists, the dams are intended to cut flood-season flow on the lower Mekong by a quarter — enough to halve the flood pulse in Phnom Penh. Hydrologists are divided about whether this is enough to end the reverse flow of the Tonle Sap. What is certain is that it will drastically reduce the amount of water backing up into the flooded forest, which will dry out — with severe consequences for the Mekong fishery.

The construction of the dams is a political as well as an ecological travesty. China is blocking the river without any prior consultation with its neighbors. In 1995 Vietnam, Cambodia, Laos, and Thailand — the four downstream nations on the river — formed the Mekong River Commission as a forum to consult on the river’s future. China never joined. It still refuses to. And it has never even discussed its dam plans with the commission. It is a vivid example of China’s disregard for its neighbors, who are too scared of Big Brother’s clout to speak out.

China is not alone as an upstream bully on the world’s great international rivers. Ask the Iraqis about Turkey’s dam construction on the Tigris and Euphrates, or the Mexicans about the U.S. on the Colorado. We badly need international law to protect downstream nations — something the U.N. agreed was necessary a decade ago but has never acted on. But even more, we need international initiatives to protect the ecological integrity of the world’s last great wild rivers. Starting with the Mekong.

POSTED ON 16 Jun 2009 IN Climate Energy Pollution & Health Pollution & Health Sustainability Water Asia 


I have been to Tonle Sap lake and I cannot believe what China is doing. It will affect millions of people downstream who are only eating one or two meals a day as it is. All these countries are going to be severely affected. The rice paddies in Vietnam and Laos were not even mentioned. I wonder how many beautiful waterfalls in Laos and Thailand will be affected not too mention fishing there on nearby Moon River in Ubon Ratchathani province on the Laos border. Every month I find something significant about China that reminds me they are a selfish communist country. This is a travesty!
Posted by Toby on 07 Jul 2009

Nevermind the river fishery and its protein. The Mekong flood helps irrigate the paddies of these four Southeast Asian countries. Those paddies produce the rice that feeds almost 200 million people, every day. Thailand is the world's top rice exporter, helping feed Indonesia, the United States, and my native Singapore too. Reduced rice production will see food prices driven upwards, and by pessimistic estimates may even drive mainland Southeast Asia to food shortages. Do we really need another couple hundred million more starving people?
Posted by Tse Yang Lim on 09 Jul 2009

This sad tale was extensively covered in Fred’s book When The Rivers Run Dry. This is sure to be tragic and devastating if nothing is done. It means big changes ahead for SE Asia on so many levels. Reading Fred’s book I got the impression water rights is at the root of many current and future struggles on our planet. Think the Mid East, Africa, Pakistan and India….the list goes on.

An unbelievably important book that everyone should read.

Posted by KJ on 15 Jul 2009

UN is a good organization to look up to for matters for such international concern. However, as we have learned in recent world developments, UN power to play fair is seriously impaired by the veto power allotted to the 5 permanent members.

China should at the very least share generated power with the downstream nations so that they can benefit from the project too. China is a regional superpower but it should play fair with its neighbors and let them have a say in the design of the dam which would displace millions of people in the downstream nations.
Posted by Amy on 22 Aug 2009

The bullying of Big Brothers is not only in the present case.The UN should stand in defense of the smaller countries to make the world look like human society. But now, when we are too much worried about carbon control, we can better suggest other ways to mitigate the adverse results of dams instead of directly opposing carbon-less energy production. Fisheries can be promoted in reservoirs and water supply to lower regions can be regulated by enforcing powerful international laws.
Posted by Padam Pande on 19 Sep 2009

Any big country showing bullying behavior towards its smaller neighbours wouldn't do good to itself in the long run. The UN must play the mediator to provide justice. But, at a time when the world is alarmingly seeking an alternative to fossil fuel to mitigate greenhouse gases, is it high time to speak out opinions against a hydro electricity project at any cost? Can't the losses be compensated in any other ways?
Posted by Padam Pande on 21 Sep 2009

This sad tale was extensively covered in Fred’s book When The Rivers Run Dry. This is sure to be tragic and devastating if nothing is done. It means big changes ahead for SE Asia on so many levels. Reading Fred’s book I got the impression water rights is at the root of many current and future struggles on our planet. Think the Mid East, Africa, Pakistan and India….the list goes on.
Posted by rhys hampson on 23 Sep 2009

Besides all of the obvious negative impacts that damming the river will create, there are several positive impacts as well. For one, it provides cheap power for many countries, thousands of jobs, and they can control flooding.
Posted by Kieran on 23 Sep 2009

Comments have been closed on this feature.
Fred Pearce is a freelance author and journalist based in the UK. He is environment consultant for New Scientist magazine and author of the recent books When The Rivers Run Dry and With Speed and Violence. His latest book is Confessions of an Eco-Sinner: Tracking Down the Sources of My Stuff (Beacon Press, 2008). In earlier articles for Yale Environment 360 Pearce has written that overconsumption, not overpopulation, is the bigger global problem, and that developing countries must be held accountable as global climate talks resume.



How Tracking Product Sources
May Help Save World’s Forests

Global businesses are increasingly pledging to obtain key commodities only from sources that do not contribute to deforestation. Now, nonprofit groups are deploying data tools that help hold these companies to their promises by tracing the origins of everything from soy to timber to beef.

With Trump, China Emerges
As Global Leader on Climate

With Donald Trump threatening to withdraw from the Paris Agreement, China is ready to assume leadership of the world’s climate efforts. For China, it is a matter of self-interest – reducing the choking pollution in its cities and seizing the economic opportunities of a low-carbon future.

For China’s Polluted Megacities,
A Focus on Slashing Emissions

The booming industrial center of Shenzhen is a showcase for Chinese efforts to cut CO2 emissions and make the nation's burgeoning cities more livable. But it remains to be seen whether China's runaway industrial development can give way to a low-carbon future.

Hard-Pressed Rust Belt Cities
Go Green to Aid Urban Revival

Gary, Indiana is joining Detroit and other fading U.S. industrial centers in an effort to turn abandoned neighborhoods and factory sites into gardens, parks, and forests. In addition to the environmental benefits, these greening initiatives may help catalyze an economic recovery.

In Istanbul’s Ancient Gardens,
A Battle for Future Harvests

Development pressures are threatening Istanbul's centuries-old gardens, which have produced food for the city's markets since Byzantine times. A coalition of gardeners and environmentalists is fighting to preserve them.


MORE IN Reports

How Tracking Product Sources
May Help Save World’s Forests

by fred pearce
Global businesses are increasingly pledging to obtain key commodities only from sources that do not contribute to deforestation. Now, nonprofit groups are deploying data tools that help hold these companies to their promises by tracing the origins of everything from soy to timber to beef.

How Warming Threatens the Genetic
Diversity of Species, and Why It Matters

by jim robbins
Research on stoneflies in Glacier National Park indicates that global warming is reducing the genetic diversity of some species, compromising their ability to evolve as conditions change. These findings have major implications for how biodiversity will be affected by climate change.

Full Speed Ahead: Shipping
Plans Grow as Arctic Ice Fades

by ed struzik
Russia, China, and other nations are stepping up preparations for the day when large numbers of cargo ships will be traversing a once-icebound Arctic Ocean. But with vessels already plying these waters, experts say the time is now to prepare for the inevitable environmental fallout.

How Forensics Are Boosting
Battle Against Wildlife Trade

by heather millar
From rapid genetic analysis to spectrography, high-tech tools are being used to track down and prosecute perpetrators of the illegal wildlife trade. The new advances in forensics offer promise in stopping the trafficking in endangered species.

African Wetlands Project: A Win
For the Climate and the People?

by winifred bird
In Senegal and other developing countries, multinational companies are investing in programs to restore mangrove forests and other wetlands that sequester carbon. But critics say these initiatives should not focus on global climate goals at the expense of the local people’s livelihoods.

Ghost Forests: How Rising Seas
Are Killing Southern Woodlands

by roger real drouin
A steady increase in sea levels is pushing saltwater into U.S. wetlands, killing trees from Florida as far north as New Jersey. But with sea level projected to rise by as much as six feet this century, the destruction of coastal forests is expected to become a worsening problem worldwide.

On College Campuses, Signs of
Progress on Renewable Energy

by ben goldfarb
U.S. colleges and universities are increasingly deploying solar arrays and other forms of renewable energy. Yet most institutions have a long way to go if they are to meet their goal of being carbon neutral in the coming decades.

For European Wind Industry,
Offshore Projects Are Booming

by christian schwägerl
As Europe’s wind energy production rises dramatically, offshore turbines are proliferating from the Irish Sea to the Baltic Sea. It’s all part of the European Union’s strong push away from fossil fuels and toward renewables.

In New Ozone Alert, A Warning
Of Harm to Plants and to People

by jim robbins
Scientists are still trying to unravel the damaging effects of ground-level ozone on life on earth. But as the world warms, their concerns about the impact of this highly toxic, pollution-caused gas are growing.

The Rising Environmental Toll
Of China’s Offshore Island Grab

by mike ives
To stake its claim in the strategic South China Sea, China is building airstrips, ports, and other facilities on disputed islands and reefs. Scientists say the activities are destroying key coral reef ecosystems and will heighten the risks of a fisheries collapse in the region.

e360 digest
Yale Environment 360 is
a publication of the
Yale School of Forestry
& Environmental Studies


Donate to Yale Environment 360
Yale Environment 360 Newsletter



About e360
Submission Guidelines

E360 en Español

Universia partnership
Yale Environment 360 articles are now available in Spanish and Portuguese on Universia, the online educational network.
Visit the site.


e360 Digest
Video Reports


Business & Innovation
Policy & Politics
Pollution & Health
Science & Technology


Antarctica and the Arctic
Central & South America
Middle East
North America

e360 VIDEO

A look at how acidifying oceans could threaten the Dungeness crab, one of the most valuable fisheries on the U.S. West Coast.
Watch the video.


The latest
from Yale
Environment 360
is now available for mobile devices at e360.yale.edu/mobile.


An aerial view of why Europe’s per capita carbon emissions are less than 50 percent of those in the U.S.
View the photos.

e360 VIDEO

An indigenous tribe’s deadly fight to save its ancestral land in the Amazon rainforest from logging.
Learn more.

e360 VIDEO

Food waste
An e360 video series looks at the staggering amount of food wasted in the U.S. – a problem with major human and environmental costs.
Watch the video.

e360 VIDEO

Choco rainforest Cacao
Residents of the Chocó Rainforest in Ecuador are choosing to plant cacao over logging in an effort to slow deforestation.
Watch the video.

e360 VIDEO

Tribal people and ranchers join together to stop a project that would haul coal across their Montana land.
Watch the video.