In Cambodia, a Battered Mekong Defies Doomsday Predictions

Among them is a new government-backed proposal that seeks to turn a particularly bio-rich stretch of the river in northern Cambodia into a UNESCO World Heritage Site. Such a designation, reserved for sites of great scientific or cultural significance, means this part of the river should, at least on paper, enjoy protection from various forms of development, including dam building. And so some conservationists are now offering a more hopeful, if cautious, message: that with better decision-making and management, the river may continue to deliver the bounty of natural resources it has for millennia.

“The Mekong is not dead,” says Sudeep Chandra, director of the Global Water Center at the University of Nevada, Reno, who leads the USAID-funded Wonders of the Mekong research project. “We’ve seen huge environmental pressures causing the Mekong to dry up and fisheries to almost collapse. And yet we also see the incredible resilience of this river in the face of those threats.”

Originating in the Tibetan highlands and winding its way through six countries before disgorging into the South China Sea, the 2,700-mile-long Mekong River is home to the world’s largest inland fishery, with about 1,000 species of fish. Many of the 70 million people living in the basin rely on the river for their livelihoods, whether that is farming, fishing, or other occupations. “A case could be made that the Mekong is the world’s most important river,” says Chandra.

The river’s extraordinary productivity is linked to a giant flood pulse that, in the wet season, can raise water levels 40 feet. With the increase comes sediment that’s essential to agriculture as well as vast numbers of young fish, which are swept into Cambodia’s vital Tonle Sap Lake and other floodplains where they feed and grow.

But the river’s natural flow regime has been increasingly disrupted by dams, especially those that China began building in the early 1990s in the Upper Mekong and which the country has operated with little regard for downstream impacts. A subsequent frenzy of dam building in Laos and elsewhere, mostly on tributaries to the Mekong, has greatly exacerbated the problem, with dams blocking fish from completing their natural migrations. Already under extreme pressure from overfishing, some fish populations have plummeted, especially large species like the critically endangered Mekong giant catfish, which can grow to 10 feet in length and more than 600 pounds, but is now on the brink of extinction.

With climate change intensifying, monsoon rains have become more unpredictable. During droughts in 2019 and 2020, the flow of water from the Mekong into Tonle Sap, the largest lake in Southeast Asia, dried up, and dam operators made matters worse by holding back much of their impounded water for their own economic gains. As a result, mass deaths of fish due to shallow and oxygen-poor water were reported in the lake, and many of the hundreds of thousands of fishers operating on the lake were forced to abandon their work.

On the Tonle Sap River, which connects the Mekong and the lake, two thirds of the 60-something commercial “dai” operators working stationary nets, which in years past could each catch several tons of fish in just an hour, had to shut down. “The situation became so dire there were concerns these fisheries could no longer be sustained,” says Peng Bun Ngor, a fish ecologist and dean of the faculty of fisheries science at Cambodia’s Royal University of Agriculture in Phnom Penh. That would be a catastrophe for Cambodians, whose per capita fish consumption is higher than that of any other people in the world.

However, the river system caught a break with the most recent monsoon season, which runs roughly from June to November, delivering greater than average rainfall to the lower basin and the Tonle Sap Lake region. Although China continued to hold back water to counter its persisting drought, water levels in Tonle Sap rose more than one meter above recent-year averages. With the lake expanding into seasonally flooded forests, which provide excellent feeding grounds for fish, fish populations appear to have been boosted. “Overall we’re seeing more fish being caught, with a greater diversity of species and larger sizes of individual fish,” says Ngor.

On a recent visit to the lake, Ngor noticed an increase in medium- and large-size carps, including Jullien’s golden carp, also known as the isok barb, a critically endangered species. There were spottings of other rare fish too, like the Laotian shad and clown featherback, along with increases of more common fish, like the climbing perch and snakehead. Several wallagos, a catfish that can grow up to 8 feet long, could be seen jumping from the open water.

At the dai fishery, 13,000 metric tons of fish were caught last year, up 30 percent from the year before. “We’re seeing fish come back if conditions improve,” says Heng Kong, director of the Inland Fisheries Research and Development Institute of the Cambodian Fisheries Administration in Phnom Penh.

A crackdown by authorities on the use of illegal fishing methods in the lake, such as trawling and electrofishing, has also alleviated pressure on fish populations, experts say. The campaign followed a speech last year by Cambodia’s long-serving Prime Minister, Hun Sen, in which he excoriated provincial officials for failing to tackle illegal fishing. But the crackdown has also come under strong criticism. Ostensibly targeted at larger-scale commercial fishers, it has resulted in the prosecution of small-scale fishers, especially those of Vietnamese origin, for minor infractions. Many of these fishers, who have lived on and around the lake for decades, have reportedly had to flee.

Enforcement issues aside, conservationists worry that ecological improvements could be temporary if more dams are built: the drive by Laos to rapidly expand its hydropower sector shows few signs of slowing down. Preliminary construction on a dam near Luang Prabang, on the main stem of the Mekong, is underway. Laos already has two dams on the Mekong itself.

Many hydropower projects, in Laos and elsewhere, are driven by political or private interests and rarely take into account environmental costs, observers say. One example is a small dam being planned in Laos near the Cambodian border, on the Sekong River, an important Mekong tributary that has until now remained the only large free-flowing tributary in the basin.

Known as Sekong A, the dam is being constructed by a state-owned Vietnamese company, but the project is shrouded in secrecy. No formal construction contract has been put in place. “It’s essentially being built illegally,” says Brian Eyler, who monitors dam developments in the Mekong as director of the Southeast Asia program at the Stimson Center in Washington, D.C.

While the dam is expected to produce only a tiny fraction of the region’s power supply, studies show it will have a strong negative impact on fish abundance and diversity in the Sekong, as well as alter water quality and further decrease the amount of sediment and nutrients that reach the Mekong. “It’s a perfect example of a high-cost, low-benefit project,” says Eyler.

Cambodia, for its part, has begun to reconsider its own dam developments. A large dam it completed in 2019 on another major Mekong tributary, the Sesan River, has proven a costly failure, with lower-than-expected energy production and disastrous environmental impacts. Plans for two large dams along the Mekong mainstem in the northern part of the country appear to have been shelved, at least for now. Instead, the government has proposed that the roughly 100-mile stretch of river where the dams would be built be designated a UNESCO World Heritage Site in recognition of its ecological importance and biological richness.

This section of the river, which flows leisurely past sandbanks and islands covered in seasonally flooded forest, has historically spawned up to 200 billion fish each year, and its many deep pools, some of which reach a depth of 260 feet, are believed to be refuges for enormous fish, including the giant freshwater stingray.

Last year, fishers here caught a stingray weighing 661 pounds, which Guinness World Records verified as the largest freshwater fish species ever recorded. The stingray was tagged and released by a team of U.S. and Cambodian scientists as part of a first-ever regional telemetry study, which aims to learn more about fish movements and behavior.

The World Heritage Site proposal has also been described as a last-ditch effort to protect the Mekong’s remaining population of Irrawaddy River dolphins. While the last individual of a small dolphin group that lived on the Cambodia-Laos border died at the end of last year, a population of fewer than 100 individuals remains in the deep pools of Kampi, located toward the southern end of the river section proposed for protection. The pools are also a popular tourist destination.

“The dolphins symbolize the biological importance of the Mekong River, and this designation would significantly attract the attention of all the stakeholders concerned with protecting the Mekong River and its aquatic biodiversity,” says Somany Phay, a senior conservation officer with the World Wildlife Fund who also holds a senior position with the Cambodian Fisheries Administration.

There are signs that outreach efforts encouraging fishers to protect critically endangered fish are producing results. Earlier this year, fishers caught a Mekong giant catfish weighing more than 200 pounds in the Mekong River in Kang Meas district. None of the fishers in the group had ever seen such a huge catfish before. But rather than killing it and selling the meat for a sizeable profit, they decided to release it in a special ceremony, in which the fish was sprinkled with flowers and perfume before it was let go. “We knew this was a very special fish and it would be bad luck to kill it,” says one of the fishers, Thou Theary.

Giant fish are often considered good indicators of river health, so the capture of the adult giant catfish in Kang Meas sent a positive signal about the Mekong’s future. “People have been saying that the Mekong is so degraded that it cannot be fixed, but this is not true,” says Chea Seila, the Cambodian program manager for the Wonders of the Mekong project. “The Mekong River still flows, and the fish are still abundant.”