Photograph by Soe Zeya Tun, Reuters
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A fisherman on the banks of the Mekong River outside Nong Khai, Thailand, on January 10.

Photograph by Soe Zeya Tun, Reuters

Southeast Asia’s most critical river is entering uncharted waters

This river has nourished civilizations for millennia. Now it’s drying up, under attack from dam building, overfishing, and sand mining.

For months now, a single, rare Irrawaddy river dolphin, apparently entangled in a fishing net and disoriented, has been spotted in Southeast Asia’s struggling Mekong River, far from its normal habitat in northern Cambodia. Conservationists are scrambling to come up with a plan to help the critically endangered animal before it’s too late, but time is running out.

Dolphins sometimes play metaphorical roles in Cambodian folklore. This one, astray and fading, could be an analogy for how the Mekong has lost its way. As the fate of the dolphin hangs in the balance, so does the future of the Mekong, with signs growing increasingly stronger that a river sustaining one of the richest ecosystems on Earth is being strangled on a basin-wide scale.

For years people have warned that an environmental crisis looms along the 2,700-mile-long waterway, which runs through six Asian countries. The Mekong could not withstand the onslaught of dam building, overfishing, and sand mining forever, they argued. Yet somehow the river has, so far, powered through, delivering an almost indescribable bounty to the more than 60 million people who depend on it for their livelihoods. (Dramatic photos show how sand mining threatens a way of life in Southeast Asia)

Each orange dot represents a dam on the Mekong River or one of its tributaries.

Then, in 2019 things took a turn for the worse. It started when critical monsoon rains failed to arrive as usual in late May. As drought gripped the region, water levels in the Mekong dropped to their lowest in 100 years. The rains finally came, but they didn’t last as long as usual, and the drought continued.

In recent months strange things have begun to happen. In some places in the north, the mighty Mekong has slowed almost to a trickle. The water has changed to an ominous color and begun filling with globs of algae. Catches from the world’s largest inland fishery have dwindled, and the fish that are being caught are so emaciated that they can only be used to feed other fish.

“Everywhere you look there are indications that this river, which has provided for so many, for so long, is at a breaking point,” says Zeb Hogan, a fish biologist at the University of Nevada, Reno, and a National Geographic Explorer.

Now, with the Mekong entering into unchartered waters, Hogan and others are asking: What lies around the bend for a river that has nourished civilizations for thousands of years?

90 Days in 90 Seconds: Life on the Mekong River While on assignment for  National Geographic magazine, photographer David Guttenfelder captured one second of video to represent each day in the field. Experience his whole journey in a minute and a half.

Click to read more about the Mekong River online in National Geographic magazine.

Natural fluctuations disrupted

Originating in the icy headwaters of the Tibetan highlands, the Mekong River flows through the steep canyons of China, known as the upper basin, through lower basin countries Myanmar, Laos, Thailand, and Cambodia, before fanning across an expansive delta in Vietnam and emptying into the South China Sea.

It is a deeply interconnected river in which changes in one place can have major consequences elsewhere. Its great productivity—it is home to more than 1,000 species of fish, with many yet to be discovered—depends in large part on seasonal floods that create ideal habitats for fish and water birds, and carry sediment crucial to agriculture downriver.

But that natural ebb and flow is increasingly being disrupted, experts say, with the effects of hydropower dams and climate change becoming ever more evident.

A large part of the problem has long been China, which operates 11 dams on the Mekong. During times of extreme drought, like now, China’s portion of the river contributes up to half of the river’s flow, with the dams holding back more than 12 trillion gallons of water, severely disrupting the water flow downstream.

“When drought sets in, China effectively controls the flow of the river,” says Brian Eyler, director of the Southeast Asia program at The Stimson Center in Washington, D.C.

Fishers and farmers in northern Thailand have long had to deal with wild fluctuations in river flow as China stores and releases water from its dams. Such changes have a detrimental impact on fish migration, and sudden increases in water level often wash away crops, livestock, and equipment, disrupting rural economies.

Lately, the situation has grown more dire. After China halved output from its Jinghong dam during several days of testing earlier this month, the water level dropped so low in some stretches of the river that it became virtually unrecognizable, with giant rocks and sandbars exposed in the middle of the wide waterway.

“I’ve never seen anything like this,” says Chainarong Setthachau, an environmentalist at Thailand’s Mahasarakham University, who has studied the river for decades.

Hungry water, starving water

The environmental impact from dams is set to increase as Laos, the poorest country in the region, continues on a path to turn itself into “the battery of Southeast Asia” by building hundreds of new hydroplants in the coming years. It is already operating more than 60 dams on Mekong tributaries, and late last year two of the several dams it has planned for the main stem of the river, which has so far remained undammed below China, came online.

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This aerial image, taken on October 28, 2019, shows the Mekong River more than 185 miles from the Xayaburi dam in Laos. Dessicated river beds downstream from the dam have stirred outcry from conservationists and villagers who rely on the diverse ecosystem for food and livelihoods.

The larger of those two, the Xayaburi dam, had long been stuck in a legal battle over concerns that it would hurt fish migration and communities downstream. The dam’s developer, a Thai company called CK Power, claims it has spent more than $600 million to mitigate negative impacts, including installing fish ladders and special gates for sediment to pass, though many environmentalists remain unconvinced.

Soon after the dam began operating, the normally chocolate-colored Mekong began to turn a brilliant blue in parts farther south, a sign that the river had been stripped of the brown sediment it normally transports and which enriches the soils of the basin. Such conditions are known as “hungry water” and can be highly destructive, as the water eats away at river banks and causes erosion.

Many ecologists suspect sediment is being blocked by the Xayaburi dam, though it may also be that the weak river flow causes sediment to drop to the bottom, with blue water coming in from tributaries to overpower the brown water. It is very likely, however, that the plant is not releasing as much water as it is taking in, contributing to the low water level downstream.

“In these drought conditions, the dam operators will keep as much water as they can,” says Thanapon Piman, who is a research fellow with the Stockholm Environment Institute in Bangkok.

The clear, slow-flowing water has also allowed algae to grow on the sand and bedrock bottom of the river. Normally, this growth would be flushed away by the current, but this is not happening and in the last couple of weeks much of the margins of the river in Thailand and Laos have turned completely green.

At the same time, the hungry water has moved into Cambodia. “We worry that it will spread further,” says So Nam, chief environmental management officer at the inter-governmental Mekong River Commission. “If this extremely low water continues, things may not become better until the onset of the next rainy season.”

Beating heart slowing down

Relying on the rescue of Mother Nature, however, has become increasingly fraught in the Mekong region, which studies show is particularly vulnerable to climate change. The current drought is driven by El Niño conditions—the warm, wet half of a naturally occurring weather cycle—that are predicted to last several years and may be exacerbated by warming temperatures.

When it comes to fishing, no country is feeling the heat more than Cambodia. It is home to Southeast Asia’s largest lake, the Tonle Sap, also known as the “beating heart of the Mekong.” Each year, after the rains begin, the Tonle Sap, which connects to the Mekong through its eponymous river, expands many times in size and provides vital habitat for fish to feed and grow. It is of immense commercial importance, with normally at least 500,000 tons of fish drawn from it each year—more than from all of North America’s rivers and lakes combined.

Last year, however, the water from the Mekong into the Tonle Sap came so late and receded so early that large parts of the lake never filled up. Mass deaths of fish were reported because of shallow and oxygen-poor water. According to one estimate, fish catches may have declined by up to 90 percent in Tonle Sap, forcing many fishers to abandon their work. Of those who continue, many are no longer catching fish for human consumption, but rather fish larvae to feed fish farms, says Rohany Isa, a Cambodian journalist who covers Tonle Sap issues.

The poor fishing conditions have continued into the current season, with much less water—and fish—moving down the Tonle Sap River. This is normally the time of the largest animal migration on Earth, when billions of fish, starting with the critically endangered Mekong giant catfish, make their way back to the Mekong. (Read about river sanctuarites helping the giant catfish recover.)

But fishers say they have not only not seen any of the endangered giants in recent months, but that catches of the staple trey riel, a mud carp known as “money fish” in Cambodia, have been much smaller. More than one-third of the 60-something commercial “dai” operators, who work stationary nets in the Tonle Sap River, did not even begin fishing this season.

During a visit last month to one of the dais, located 40 miles north of the capital of Phnom Penh, workers dumped what appeared to be a massive catch of trey riel onto the wooden deck of a floating house boat. But, as the operations manager Sue Mao explained, the catch was far less than what a dai is capable of pulling in during good years: over five tons of fish in just an hour. The mud carp also appeared substantially smaller than usual.

“They’re too skinny to make prahok,” said Mao, referring to the fish paste that’s a Cambodian staple food.

By the time the next peak time for fishing rolled around, earlier this month, dai catches had declined even further, and the majority of the operators had decided to close down.

Hogan, who leads a USAID project, “Wonders of the Mekong,” worries that cumulative years of drought will see populations of many fish species crash, along with the fisheries that depend on them.

“Fish can be remarkably resilient, with the ability to bounce back from naturally occurring events such as drought,” he says. “The danger now is that the river is changing in ways that are outside the bounds of natural variability.”

Eyler, The Stimson Center director, says his biggest concern is a major food shortage in the Tonle Sap. “Typically that catch translates into the world's largest for one body of water and provides the 16 million people of Cambodia with most of its protein. The price of fish in markets is skyrocketing in Cambodia and a food crisis could emerge at any moment,” he says.

Regional efforts hold hope

With the dry season having just set in, fears are that matters could deteriorate quickly. While Thai officials have warned of severe water shortages in the coming months, Cambodia could face major food deficits, observers warn. Meanwhile, worries are growing in Vietnam over the state of the delta. There, widespread erosion, caused primarily by sand mining, has led to many houses and roads collapsing, with public emergencies declared in six provinces.

Eyler says decision makers in the region have not yet realized the seriousness of the situation. “Mekong governments are not reacting fast enough to understand the oncoming crisis and work together to mitigate risk and improve resilience,” he says, adding that in many cases officials are unaware that they have tools at their disposal to provide things like drought relief.

Hogan believes that economic priorities need to shift in order for the Mekong to survive. “The river has been changed to benefit people who see it as a source of power,” he says. “That must change, so that the food, fertility, and ecosystem services provided by a healthy, connected, and free-flowing river are valued higher.”

That means stopping or at least slowing down the race to dam the Mekong, which so far doesn’t seem to be happening. While some governments, like Cambodia’s, may be reconsidering plans it has to build two dams in the northern part of the country, Laos recently announced that construction on a controversial dam it is planning close to a World Heritage Site in Luang Prabang will begin this year, ahead of schedule.

With regional cooperation considered essential to changing policies, some people are looking to the Mekong River Commission to take on a stronger role. The organization has long been seen as politically weak, because it only includes four of the basin countries and not China, which has set up its own commission, the Lancang-Mekong Cooperation. (The Mekong is called Lancang in China.)

But the two groups recently signed a pledge to work closer together. “This is a good starting point,” says Anoulak Kittikhoun, the MRC’s chief strategy and partnership officer. “China is becoming more open, which is something we welcome.”

He points out that when China conducted its testing at Jinghong Dam earlier this month, it gave a week’s advance notice to downstream countries to expect reduced water flow. “In the past, it did not do this,” says Kittikhoun.

And most conservationists seem to agree that it is not too late to save the Mekong River. “We’ve seen the Mekong getting injured, and more and more devastation happening here and there,” says Pianporn Deetes, a campaigner with International Rivers. “But it’s not dying. The Mekong's incalculable ecological value can be restored and back to function to sustain the region's future.”