It will be a giant, stretching across the mighty Mekong River. Standing 32.6 metres tall and 820m wide, the $3.8 billion Xayaburi dam in Laos could supply electricity to more than three quarters of a million homes in Thailand. And when it’s completed in 2019, it will be the most controversial power project in the region.

Since the plan was released in 2010 to construct the hydroelectric plant, geologists and environmentalists have voiced concerns about safety and the effects the mega-dam will have on neighbours Cambodia, Vietnam and Thailand. They have highlighted the risks of seismic activity in the area and the threat to the fishing industry on the 3,100-mile long (4,900 kilometres) Mekong River, which flows from the Tibetan steppes into southern China on its way to Myanmar, Laos, Thailand, Cambodia and Vietnam.

“Previous earthquakes near the Xayaburi dam site should have served as a warning for Laos and the Thai dam company,” said Ame Trandem, the Southeast Asia programme director for the conservation group International Rivers. “It is completely irresponsible to push forward with a project located in a seismically unpredictable zone.”

During the past seven years, the area around the Xayaburi dam project has been shaken by earthquakes. A 6.9 magnitude quake hit Shan state in Myanmar. A 4.6 tremor only 48 kilometres away from the proposed project was recorded in 2007, while a 6.3 convulsion was reported in the Xayaburi area in the same year.

Naturally, this has alarmed Dr Punya Charusiri, who heads earthquake studies at Chulalongkorn University’s Department of Geology. The Thai scientist has identified an active fault close to Xayaburi town about 30km from the site. “I am worried that many people from the town would be affected. But I am not able to predict how much damage would be done to the dam itself, which is built on an ‘inactive fault’,” he said.

The risk factor is certainly there. During the 7.9 magnitude earthquake in Sichaun, China in 2008, the walls of the Zipingu dam were badly damaged and came close to unleashing a second disaster of epic proportions.

“In a worse case scenario, if a [major] earthquake happened right under the [Xayaburi] dam, then nobody knows,” said Dr Sampan Singharajwaranpan, a seismologist and the dean of sciences at Chiang Mai University.

Safety, of course, is not the only concern. Fears are growing about the impact on the environment and ecology of the region when the Xayaburi dam, one of nine hydropower plants planned by the Laos government, is up and running. More than 30 million people in Cambodia and Vietnam rely on the Mekong River for their livelihoods. Rice and fish exports could be threatened in the inland waterways, which generate up to $3.9bn in revenue a year, equivalent to a quarter of the world’s annual catch.

Up to 40 species, such as the giant catfish, are under further threats from the dam, according to a report commissioned by the World Wildlife Fund (WWF). “Mortality is likely if fish pass through dam turbines [and] . . . the cumulative impacts of the dam are a serious threat,” said Zeb Hogan, an associate research professor at the University of Nevada in the US, and author of the report. “A fish the size of a Mekong giant catfish will simply not be able to swim across a large barrier like a dam to reach the spawning grounds.”

The Cambodian government is also anxious to avoid fish stocks being damaged. This in turn could lead to dietary problems if the industry is badly hit. “[Fish provide] 76 per cent of animal intake, 37 per cent of protein intake, 37 per cent of iron intake and 28 per cent of fats intake of the Cambodian population,” a study by the Cambodian Fisheries Administration (CFA), a government body, revealed.

Nao Thuok, the director of the CFA, underlined Cambodia’s concerns when he said the “protection of fisheries in the Mekong should be regarded as an issue of national security”. The stakes are so high, a joint declaration, released in March, from 39 non-governmental organisations (NGOs) in Cambodia, Vietnam, Thailand and Australia set a one year deadline for the Laos and Thailand governments to scrap the project. “There is still essentially one year left to stop the dam as construction on the Xayaburi [power project’s] final dam across the Mekong River will begin in 2015,” said Trandem of International Rivers.

As the clock ticks down, the pressure is building on CH. Karnchang, the Thai group that will construct the dam, and partner Poyry Energy, part of the Finnish-based international engineering company and consultants Poyry. The Thai government has also been dragged into the dispute after agreeing to buy 95 per cent of the electricity generated at the hydropower plant.

One major concern aired by independent geologists has been the lack of transparency from CH. Karnchang and Poyry Energy about crucial seismic studies. Te Navuth, the secretary general of Cambodia’s National Mekong Committee, had called for “an independent research team [to] assess the risk of earthquakes and dam safety” back in 2011.

Two years after construction began, the Mekong River Commission (MRC) received “[a] seismic hazard assessment” which was drafted by Poyry Energy and AF Consult, the Swiss company based in Zurich. The MRC referred the “assessment” to an independent expert, but so far the Cambodian government has yet to see the report.

“The seismic hazard at the Xayaburi dam site has been studied thoroughly and the dam, the powerhouse, and the spillway will be designed against earthquakes, according to the latest seismic design guidelines prepared by the International Commission on Large Dams [ICOLD],” said Dr Martin Wieland, the managing Director of Poyry Energy.

Critics of the project have expressed disquiet about ICOLD and claimed that it is not an independent research body, but a forum for the dam engineering lobby largely funded by hydropower companies. Dr Wieland, of Poyry, is also chairman of the committee on Seismic Aspects of Dam Design for ICOLD in charge of seismic guidelines.

“The CH. Karnchang people assumed that the faults closest to the dam-site are inactive, and so they believe it is quite safe,” said Dr Punya, who has also worked for the CH. Karnchang group. “But there is an active fault and it is located within a 30km radius. Construction should never have been started before the research into the danger has been completed.”

As the row continues, regional government heavyweights have warned of the dangers ahead if the Xayaburi project is completed. “We have to protect our interests,” said Lim Kean Hor, the Minister of Water Resources and Meteorology in the Cambodian government. “We will not allow [construction] if there will be a serious impact.”

Just like the huge scale of the Xayaburi hydropower plant, the arguments against the project have grown from a trickle to a tidal wave. What happens next could change the course of the Mekong River for generations to come.

Tom Fawthrop is a freelance journalist and filmmaker, and directed the documentary, Where Have All the Fish Gone? Killing the Mekong Dam by Dam Eureka Films. He can be contacted at [email protected]