Archive for August 16th, 2011

August 16, 2011

Can Damming the Mekong Power a Better Life to Laos? ‎- Mayhem on the Mekong‎


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By Brendan Brady / Xayaburi ProvinceFriday, Aug. 12, 2011


Vendors pack up for the day at a ferry crossing upstream from the proposed site of the Xayaburi dam in Laos. Brendan Brady

The 1,170-mile (1,880 km) stretch of the Mekong River that snakes through Laos has long been a quiet backwater used for small-scale domestic trade, localized fishing and folklore. In recent years, however, it has become the focus of a new purpose. “A dam is what I hope for most,” says Samboun Bounkeo, the thickly built chief of Thalon, a sloping village of dirt paths and thatched-roof riverfront homes in northern Laos. A stable supply of electricity, paved roads, new job opportunities and potentially much more is what a dam offers, he says. For families living on several hundred dollars per year, such development is exceedingly attractive.

Laos is among the poorest and least developed countries in Asia, and its communist government contends that hydropower, along with revenues generated from exporting it, can underwrite much of the country’s progress. In many ways, Laos is tailor-made for hydropower development. Rivers and rainfall — the basic ingredients — are plentiful, and the mountainous landscape offers a natural means of generating the hydraulic momentum that can be transformed into electricity. The government’s emphasis on cultivating hydropower, therefore, is “natural,” says Viraphonh Viravong, the director of the Department of Electricity who regularly visits various sites in Laos tapped for new dams. So, too, says Viraphonh, is it logical that Laos would expand the scope and scale of its dams in order to benefit from economies of scale. (See pictures of life on the shores of the Mekong.)

But such escalation, say observers, could have dire consequences. At the crux of the controversy is the government’s plan to introduce dams along the lower mainstream channel of the Mekong. As the river’s widest and only continuous passage from beginning to end — and the spine that connects the many tributaries making up the wider river system — the main channel and its flow are most essential to the Mekong’s health. In the late 1980s, China was the first country to install dams along the main channel, though at the time its projects drew little protest from governments of nations downstream. But further scientific research and the lobbying of environmental groups have drawn greater attention to the intensified risks of manipulating the mainstream, making it a highly controversial and, until now, an avoided undertaking.

The first of Laos’ nine proposed mainstream dams — a $3.5 billion, 1,260-megawatt project in Xayaburi province — has caused political turbulence downstream and raised fundamental concerns about the fate of the mighty river and those who live off of it. In Laos and the other countries sharing the Mekong south of China, including Thailand, Cambodia and Vietnam, tens of millions of people depend on the river for fish and irrigation. Experts warn that this series of mainstream dams will block migration routes necessary for fish spawning and impede the flow of sediment that fertilizes farmland. Cambodia’s Tonle Sap Lake, for instance, holds one of the largest freshwater fisheries in the world, and the copious rice harvest of Vietnam’s fertile delta, where the Mekong meets the sea, makes that country the world’s second largest rice exporter.

These warnings haven’t found much ground within Laos itself. “The government has shown us a plan that will improve our lives,” says Chan, a middle-aged woman who operates a food stall at a ferry crossing upstream from the site of the first proposed dam. Government officials who recently visited her community to discuss the project clearly left a good impression: she says they told her the dam won’t materially affect the river, and those with riverside businesses forced to relocate because of rising water levels from the dam will be compensated.

Several miles upstream from the chosen site for the first dam, in Thalon village, the chief, Samboun, is similarly content with the project. “I don’t have any concerns about the dam because the government has conducted a workshop on this,” he says, intoning a refrain among many communities in Laos who have been told by authorities that the dam will deliver them modernity at little cost. He says his village will gain access to dependable electricity year-round and jobs at the dam complex as well as receive public investments in roads, schools and hospitals from hydropower revenue. And, he adds, “As far as I know, the dam here won’t have a negative impact on neighboring countries.” (See pictures of new species found on the Mekong.)

This upbeat — and incomplete — assessment was echoed in a study released in March, commissioned by the Thai construction company that was contracted by Laos’ government to build the dam. The report, roundly condemned by environmental groups, looked no farther than several miles downstream in considering the dam’s impact, even though experts believe it will reach much farther. It ignored, environmental groups like WWF and International Rivers noted, existing scientific research on the Mekong ecosystem and overlooked entirely the issue of the dam’s effect on sediment movements.

In fact, outside of Laos, warnings about the Xayaburi dam, as it’s known, have come from far and wide. Environmental and human-rights groups in Thailand and Cambodia have petitioned for its construction on the dam to stop. Even Vietnam broke the solidarity of silence that typically precludes public criticism between the fellow communist states, running a series of articles in its state-run newspapers that sounded alarms against its neighbor’s hydropower plans. “The potential impacts are enormous,” says Barend Frielink, the chief economist in Laos for the Asian Development Bank (ADB), which typically has supported extensive dam construction in Laos. (The ADB says the country’s tributaries offer sufficient potential, with far less risk, for robust hydropower development).

The evidence behind their concerns is hard to ignore. A several-hundred-page report published last year by the International Centre for Environmental Management said the proposed cascade of mainstream dams through Laos would cause a “fundamental break” in the Mekong’s “equilibrium.” The Australian organization was commissioned to carry out its 16-month assessment by the Mekong River Commission, a consultative body created in 1995 by Thailand, Cambodia, Vietnam and Laos for collective management of the river. The report predicted a litany of grim consequences, including a 25% loss in the load of sediment that would reach the lower stretches of the river and a 16% to 32% drop in fish stocks. It called for a 10-year moratorium on any such projects to give time for more detailed research on their impact.

A subsequent report, published in March by the Mekong River Commission itself, found that, from the Xayaburi dam alone, the migrations of anywhere from 23 to 100 species of fish would be restricted, and the river’s iconic giant catfish, which can span 10 ft. (3 m) and weigh more than 600 lb. (270 kg), would likely fall extinct. The dam developer’s proposal to install “fish ladders” — a series of graduating steps designed to invite fish to take successive leaps to bypass the dam wall — has been received with extreme skepticism by river biologists, who point out that such devices have only been used successfully with salmon, which are unique in their jumping abilities. “We should not use the Mekong as a laboratory to prove this technology,” says Trang Dang Thuy, who heads the WWF’s Sustainable Hydropower program in Laos. The commission’s report also estimated that the dam’s power output would drastically diminish within decades from silt accumulation in the dam’s reservoir.

The momentum of Laos’ hydropower ambitions appears to be stalled by the growing chorus of opposition buttressed by these findings. In a meeting of the Mekong River Commission in April, representatives of Thailand, Cambodia and Vietnam demanded more information on the dam’s impact and kicked the issue up to the ministerial level. (The rising opposition of Laos’ neighbors is complicated given that it is, in part, their interest in importing electricity that has spurred Laos’ enlarged hydropower scheme.) Then in May the Lao government said it would defer its decision on the dam, pending further research. At the end of last month, the government reiterated its stance to reassess the Xayaburi dam, according to media reports from Bali, where U.S. Secretary of State Hillary Clinton, visiting for regional talks, called the suspension “a forward-leaning position.” The electricity department director, Viraphonh, echoes the government’s official, seemingly balanced position. “The Laos government policy is very clear: when you want to develop a project, first of all, the benefit needs to be identified for the local people,” he says. “The second part is, What is the national benefit? Then we talk about the regional benefit.”

But the sincerity of the government’s public posture is challenged by evidence that it has quietly green-lighted the project. In a letter obtained by TIME that is postmarked June 8 and addressed to the Xayaburi’s developer, the head of Laos’ energy department says the government has “provided opportunity” for its neighbors to “evaluate, discuss and comment on the Xayaburi Project,” and “we hereby confirm that any necessary step in relation to the 1995 Mekong Agreement has been duly taken in a spirit of cooperation and working together of all relevant parties.” The next day, the developer, Thailand’s CH. Karnchang Public Co., told its power purchaser that it was “now ready to execute” their deal. And work has continued unabated on an access road and work camp near the site of the proposed Xayaburi dam.

The turn of events has raised questions about whether the government double-dealed from the get-go, and cast further doubt on the whole concept of regional cooperation on the Mekong. “If you need a specific agreement before you can do something, nothing happens,” says Viraphonh. “Whether it’s good or bad, I don’t know, but there is no development.” For fishermen in Cambodia and farmers in Vietnam hovering at the poverty line, how widely Laos chooses to define development could be life-changing.


Mayhem on the Mekong

In Science Magazine

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Science 12 August 2011:
Vol. 333 no. 6044 pp. 814-818
DOI: 10.1126/science.333.6044.814


Richard Stone

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Hydropower dams planned for the lower Mekong could damage ecosystems and erode food security across the river basin.

VIENTIANE, LAOS—Flooding of biblical proportions is a way of life for villagers in the region around Cambodia’s Tonlé Sap Lake. Each summer, the lake expands from an area smaller than Rhode Island to a Connecticut-sized basin—from 2500 km2 to as much as 15,000 km2. Average depth increases from 0.5 m to 8 m or more. The spectacular phenomenon occurs when the Mekong River, swollen from monsoon rains, forces a tributary, the Tonlé Sap River, to reverse course and feed the lake instead of drain it.

One million people depend on the seasonal filling and emptying of Tonlé Sap, the “Heart of Cambodia.” “It’s the biggest inland fishery on Earth,” says Kim Geheb, Mekong Basin leader for the Consultative Group on International Agricultural Research’s Challenge Program on Water and Food. During the dry season, when Tonlé Sap drains, migratory fish head upstream to spawn in deep pools in the Mekong and its tributaries; when the lake is replenished in summer, young fish descend en masse to feed. The rising water washes organic matter from the floodplain into the lake, nourishing primary productivity. “The flood pulse is the engine of the ecosystem,” says Dirk Lamberts, an aquatic ecologist at Catholic University of Leuven in Belgium.

That dynamo is now in jeopardy. Newly built dams on the upper Mekong and its tributaries are expected to modulate the river’s flow. At first the effect will be subtle. But in the next couple of decades, Tonlé Sap will begin to stabilize, models predict. A large area of permanent inundation will swallow thousands of hectares of floodplain, disrupting the ecosystem and possibly devastating the fishery.

That gloomy scenario doesn’t take into account the latest threat to Tonlé Sap and the rest of the Mekong River Basin. Leaders here in the Laotian capital are preparing to build the first dam on the lower Mekong mainstream, the 2700-km segment that wends from the China-Laos border to the South China Sea. The $3.8 billion Xayaburi Hydroelectric Power Project, slated for completion as early as 2019, would generate 1285 megawatts of electricity—enough to power a medium-sized Southeast Asian city—mostly for export to Thailand. But the plan is raising tensions. The Mekong River Commission (MRC), which includes Laos, Cambodia, Thailand, and Vietnam, requires prior consultation on any major project that might affect sustainable development on the Lower Mekong Basin (LMB). Xayaburi dam is the first major proposal to trigger such a review. And the other three MRC members are not satisfied with the information they’ve received so far from Laos.

Vietnam, expressing “deep and serious concerns,” called last April for a 10-year moratorium on hydropower development on the lower Mekong mainstream. Laos quickly deferred a final decision on Xayaburi, at least publicly. In May, Lao Prime Minister Thongsing Thammavong assured his counterpart from Vietnam that the dam would be postponed pending further studies involving international experts. That gesture won praise last month from U.S. Secretary of State Hillary Clinton at a regional meeting. “I want to urge all parties to pause on any considerations to build new dams until we are all able to do a better assessment of the likely consequences,” she said.

But Laos may not wait long. In an 8 June letter to the general contractor that will lead the dam’s construction, the director general of the Electricity Department of Laos’s Ministry of Energy and Mining declared the MRC consultation process “complete.” The letter, subsequently leaked to the press, “changed everything,” Geheb says. The powerful energy ministry, he says, has argued that Xayaburi dam’s benefits would outweigh its costs, and that environmental consequences can be mitigated.

There’s evidence Laos has already opted to forge ahead. At the dam site in Xayaburi Province 350 km north of Vientiane, preparatory work has been going on for several months. One environmental scientist who recently visited the site estimates that there are a few hundred people in the construction camp. “It’s not a small-scale operation,” he says. Some observers expect Laos to announce a new timetable for the Xayaburi dam at a meeting of MRC’s council of ministers in autumn.

The stakes are enormous. Critics fear that Xayaburi dam and 11 other hydropower projects planned for the lower Mekong would unleash a cascade of ecological changes. Beyond threatening many migratory fish with extinction, including some of the world’s largest species, the dams could collapse fisheries and destroy productive agricultural land throughout the LMB. The resulting ecosystem damage “will result in increasing food insecurity for millions of people,” declares an MRC-commissioned Strategic Environmental Assessment (SEA) of Hydropower on the Mekong Mainstream released last October. “The proposed development of the mainstream Mekong River is the most important strategic decision ever made by LMB countries on use of their shared resources.”

The dams could alter geopolitics as well. “We are strongly concerned that there may be widespread conflicts or, in the worst scenario, wars over water resource management,” Chheang Vannarith, executive director of the Cambodian Institute for Cooperation and Peace, told Voice of America last month. As Geheb says, “Laos is under savage pressure to get this right.”

Domino effect

The Mekong River is one of the few great rivers not dammed for much of its length. That’s not for lack of hydropower potential. From its headwaters in Tibet to the China-Laos border, the 2200-km-long upper Mekong, known as the Lancang River in China, drops 4000 m in elevation. The lower Mekong follows a gentler descent, losing several hundred meters in elevation.

The main Mekong dynamo could generate an estimated 53,000 MW of power. In the four LMB nations, Mekong tributaries could add up to 35,000 MW. A sizable portion of hydropower potential of the tributaries has already been tapped or will be soon. By 2015, 36 dams on LMB tributaries are expected to be operating, with roughly 30 more to come online by 2030. Critics question whether adequate mitigation measures are being implemented for the biggest Mekong tributary dam thus far, the $1.5 billion Nam Theun 2 in central Laos, which started operations last year (Science, 23 April 2010, p. 414).

Hydropower is the best way for Laos to utilize the river, says George Radosevich, an expert on international water law who as senior legal adviser to the four LMB nations helped draft the 1995 Mekong Agreement that created the MRC. Laos, he says, “contributes the most water to the Mekong system and has the least amount of irrigable land.”

By the early 1990s, Laos and Cambodia had blueprints for 11 dams and one diversion on the lower Mekong (see map). The show-stopper until recently was iffy economics. Unlike impoundment dams that use reservoirs to manipulate river flow, the 11 proposed dams are “run-of-the-river” barrages designed to slightly perturb average flow rate. They would generate electricity aplenty during the 4-month rainy season, when 75% of the Mekong’s annual flow occurs. The rest of the year, a languid Mekong would generate much less power, raising doubts about the market value of the electricity.

China’s hydropower program tipped the balance in favor of the lower Mekong dams by advancing another claimed benefit: reducing the flood pulse. In the late 1990s, China started work on a cascade of at least seven impoundment dams on the upper Mekong. Four have been completed, including 292-m-high Xiaowan, the world’s highest arch dam (see map). Although China is not an MRC member state and thus is not bound by the 1995 agreement, under international law its use of upper Mekong water must not harm downstream nations. As an MRC observer, China’s hydropower officials at commission meetings “have always emphasized the leveling out of the flood pulse as a significant benefit” of their dams, which are designed to fill their reservoirs during the rainy season and release extra water during the dry months, Geheb says.

Regular flow would allow turbines to feed the electricity grid more consistently during the dry season, and thus is a huge selling point for Laos. In 2007, Laos asked CH. Karnchang Public Co. Ltd. in Bangkok to study the feasibility of Xayaburi, the first installment of a planned six-dam cascade north of Vientiane. Xayaburi dam would be 820 m wide, 49 m high, and would create a 49-km2 reservoir extending 60 to 100 km upstream. Some 2100 villagers would be resettled. Last September, Laos informed MRC of its intention to proceed with Xayaburi, triggering the required consultation. Laos plans to award a 30-year concession to CH Karnchang, after which Laos would assume ownership of the dam. The company and Lao authorities are negotiating a power purchase agreement with the Electricity Generating Authority of Thailand, which has offered to buy about 95% of Xayaburi’s electricity.

Xayaburi dam, if built, could pave the way for the other 11 hydropower projects on the drawing board. “Whatever happens with Xayaburi will set a precedent on whether it is acceptable to go forward with other mainstream dams,” asserts Ame Trandem, Southeast Asia program director at International Rivers, a nonprofit that opposes large dams. “The scale of hydropower being proposed in the basin is truly staggering,” Geheb says.

If all 12 projects go forward, Laos would receive the lion’s share of an estimated $25 billion in foreign direct investment and 70% of electricity export revenues, or $2.6 billion a year. The landlocked country with a per capita income of under $1000 per year is counting on hydropower to alleviate poverty, raise living standards, and improve transportation for its 6 million people.

None of the MRC nations has a veto over Laos’s plans, but they have influence. Thailand and Vietnam account for 96% of the power demand of the LMB over the next 15 years and would purchase about 90% of the electricity generated by Laos’s proposed hydropower projects. “If Thailand and Vietnam decided not to purchase mainstream power, the projects—all designed for export—would be very unlikely to go ahead,” states the SEA.

The environmental costs of going forward would be steep, according to the SEA. If implemented, the 12 projects—including 11 dams that would span the river channel—would convert a staggering 55% of the lower Mekong mainstream, from northernmost to southernmost dam, into reservoirs with slow-moving water. The dams would block migratory fish, interfere with navigation, and impede nutrient-rich sediments from settling in the Mekong delta in Vietnam and in the Tonlé Sap floodplain. The SEA estimates that fisheries and agricultural losses would run $500 million a year, offset by only $30 million a year in added income from reservoir fisheries and new irrigation potential. If all envisioned LMB hydropower projects were to go forward and using worst-case assumptions, the evisceration of Mekong fisheries and loss of wetlands and other ecosystem services could result in the basin losing $274 billion in value, according to an analysis released last month by a team led by Robert Costanza, an ecological economist at Portland State University in Oregon.

Fisheries and agricultural losses in the delta, in Lake Tonlé Sap, and elsewhere could have a domino effect on nutrition and food security. In Cambodia and Laos, “up to 30% of the national protein supply would be at risk if all mainstream dams were to go ahead,” the SEA warns.

Migratory purgatory

As the first dam on the lower Mekong mainstream, Xayaburi lays down a marker for how environmental consequences of all 12 hydropower projects will be assessed. The experience so far has proved unsettling.

Last September, CH Karnchang submitted to the Lao government an environmental impact assessment on Xayaburi prepared by Bangkok-based TEAM Consulting Engineering and Management Co. The assessment acknowledges that the dam could alter the lower Mekong’s hydrology. Rebutting an earlier feasibility assessment, however, it claims that upstream of the dam, “transformation of the habitat from a river with rapids” into a “standing ecosystem due to impoundment will not occur.”

Many who study the Mekong are baffled by that assertion. In a 24 March review, the MRC Secretariat estimates that water flow rates in a Xayaburi reservoir could decline as much as 90%, from about 1 m per second to 0.1 m per second. Under proposed operating conditions, the review states, the reservoir would lose about 60% of its capacity due to sedimentation after 30 years, compromising power generation. And based on the Xayaburi dam’s current design, the reservoir would trap two key nutrients: about 40% of phosphorus and 33% of nitrogen that enter it. The review warns that the cumulative effects of Xayaburi and other lower Mekong mainstream dams on sediment and nutrient trapping “would be significant.” Less sediment in floodwater would mean less soil fertility and a loss of rice production, as well as increased riverbank erosion, says Eric Baran, a fisheries biologist with the World-Fish Center in Phnom Penh.

In this respect the Mississippi River offers a cautionary tale. “Hydropower development in the upper Mississippi River Basin over many decades has resulted in sediment deprivation to the Mississippi River delta,” says D. Phil Turnipseed, director of the U.S. Geological Survey’s National Wetlands Research Center in Lafayette, Louisiana. “Mekong River development could have the same results as we have experienced.”

Perhaps the harshest criticism is reserved for TEAM’s prognostications on how the Xayaburi dam could affect fish stocks. An appendix to the environmental impact assessment states that hydropower development on the lower Mekong mainstream “will submerge spawning and rearing habitats of migrating fish species.” It recommends that the characteristics of these habitats be identified and described “for future habitat recovery before impoundment.” But the main body of the report simply states that the Xayaburi dam would result in “no significant change” in fish spawning. That conclusion “is not substantiated by any results presented in the assessment,” Baran says.

The report presents an incomplete picture of fish species that the dam could adversely affect. TEAM drew up a list of 16 species, including five that are migratory, based on a 1994 MRC report. It supplemented that list with field surveys conducted in November 2007 and March 2008 in which it captured 54 fish species using gillnets. Based on that meager haul, the impact assessment concludes that “fish biodiversity in the project area [is] quite low.”

Critics blast that contention. TEAM’s field surveys were an “unrealistically low, restricted, and biased sampling effort,” says Baran, who with three colleagues analyzed the report for WWF Greater Mekong, an environmental advocacy group. Their 31 March review notes that the field surveys “resulted in a biodiversity assessment representing less than a third of the actual species richness in the impact area.” And the TEAM report didn’t even cite the MRC’s own Mekong Fish Database, a 2003 resource that lists 120 fish species in Xayaburi Province. According to the WWF review, field surveys in the literature raise that figure to 229 fish species that “exploit habitats upstream of the planned dam site for spawning and/or dry season refuges,” including 70 migratory species. Those migratory fish are what experts most worry about. According to Baran’s group, by the time Xayaburi dam is completed it “would obstruct about 125,000 km2 or 36% of habitats in upstream watersheds” not already obstructed by other dams.

Some charismatic species could suffer, including several of the world’s biggest freshwater fish. The Xayaburi dam could be the coup de grâce for the critically endangered Mekong giant catfish (Pangasianodon gigas), a species that can grow up to 3 meters long and weigh 300 kilograms. Because the titan’s only known spawning area is north of the Xayaburi dam site, the MRC review holds that there is a “strong possibility” the species would go extinct in the wild if the dam is built.

The dam would threaten another critically endangered leviathan, the giant pangasius (Pangasius sanitwongsei). Also known as the dog-eating catfish, giant pangasius migrate upriver and spawn in springtime at unknown grounds, says Zeb Hogan, an ecologist at the University of Nevada, Reno, who has done extensive fieldwork on the Mekong. Sightings in Laos suggest that the Xayaburi dam site “is within the migratory corridor and may be in the vicinity of a spawning area,” Hogan says, adding that it is “very likely” that the dam site is critical habitat for the giant pangasius.

Overall, the MRC says, “no large migratory species are predicted to persist” if Laos were to proceed with all six dams in the planned cascade. It adds that the dams would also obstruct smaller migratory fish that are important food sources, such as the Siamese mud carp (Henicorhynchus siamensis).

Although Xayaburi would be equipped with a pair of structures known as fish ladders, which help fish bypass dams, it’s unclear which Mekong species would be able to climb them. Fish ladder designs are geared to salmon, whose jumping abilities enable them to scale waterfalls—and ladders—more successfully than other fish, the MRC review states. According to Hogan, Xayaburi dam as currently envisioned would present an “impassable barrier” to large fish. TEAM’s environmental impact assessment “puts unsubstantiated trust in the ability of existing technology to solve the fish migration obstruction problem,” Baran adds.

Critics also blast the assessment’s narrow focus. TEAM’s field surveys extended only a few kilometers downstream, and they did not examine possible effects upstream of the reservoir. The assessment “ignores all transboundary aspects of possible impacts,” the WWF review states. The report “is flawed and does not meet international standards by far,” Baran says. Cambodia has called for a transboundary and cumulative impact assessment.

The Laos government appears ready to accept TEAM’s findings. In February, it declared in a statement that the Xayaburi dam would be “environmentally friendly” and “not have any significant impact on the Mekong mainstream,” the Associated Press reported. “I don’t think Laos has fully understood the environmental consequences,” Trandem says.


Any environmental assessment limited to Xayaburi, or even the six-dam cascade it would anchor, ignores the combined impact of all 12 hydropower projects on the lower Mekong Basin. “You can’t look at Xayaburi in isolation,” says Matti Kummu, a hydrologist at Aalto University in Finland. The SEA, prepared by the International Centre for Environmental Management in Glen Iris, Australia, provides that broader context.

Fisheries losses and erosion of food security could overshadow gains in energy security. Although the region’s fisheries data are notoriously poor and fragmented, the MRC review calculates that the few dozen tributary dams in operation in 2015 will reduce LMB’s total annual catch of roughly 2.5 million tons of fish by 17% to 23%. It predicts that the six-dam cascade would decrease yields by another 6%. And if all 11 mainstream dams come online, the SEA estimates the total loss in fish resources would be as high as 880,000 tons, or 42% compared with the 2000 baseline (see graph).

Tonlé Sap is an acute concern. The Mekong River provides 57% of the lake’s water, and alterations to its flood pulse could erode water quality and trigger die-offs of fish eggs, larvae, and even adult fish, Lamberts says. Fisheries experts, he says, blame poor catches of Siamese mud carp in recent years on hiccups in Tonlé Sap’s usually smooth filling. As dry season flows increase, models forecast a widening area of permanent inundation that would wipe out the gallery forest surrounding Tonlé Sap. “You lose that downstream vegetation, you lose a lot of the productivity,” Lamberts predicts.

Of the dozen hydropower projects planned for the lower Mekong, the farthest downstream would be Sambor, one of two dams that Cambodia plans to build. The 18-kilometer-long barrage would span a confluence where three tributaries feed the Mekong, about 200 kilometers upstream of Tonlé Sap River. “It will be vast,” Geheb says, “and in my mind, most significant. … It’s a mystery to me why the Cambodians don’t make more noise about the likely collapse of their fisheries.” The answer, says one expert, is simple economics. Cambodia’s feeble collection of taxes on fisheries means that Tonlé Sap “doesn’t contribute much to the exchequer,” he says. It doesn’t help, he says, that Cambodia’s environment ministry is “small and powerless.”

If dam building on the mainstream Mekong takes off, it will become even more important to implement technologies that mitigate ecological harm, experts say. For instance, dams can use advanced turbine designs that sharply reduce fish mortality and incorporate sluice gates that allow more sediments and nutrients to filter downstream.

A growing chorus is urging Laos to suspend work on Xayaburi until more robust data are in. Vietnam, for one, holds considerable sway with its Socialist ally. “There is a lot of room for maneuvering,” Radosevich says. Laos must proceed with caution: Under the Mekong Agreement, it could be held responsible for damages to downstream nations.

Inescapably, mainstream dams would change the river’s character. It would be a tragedy, Lamberts says, if a region that has endured war, genocide, floods, and droughts were now to sacrifice the resilience of its ecosystems.

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