The future of the Mekong River – and potentially the food and economic security of Cambodia – is up for discussion this week, with Prime Minister Hun Sen and the leaders of Vietnam, Thailand and Laos expected to make a declaration on the development of the river basin on Thursday at the end of the four-day Mekong River Commission (MRC) summit in Siem Reap.

The message conveyed to those leaders on Tuesday night, after a two-day conference with experts, civil society and country representatives from across the Mekong Basin, was to heed the results of the MRC’s landmark Council Study – a massive report assessing the impacts of hydropower development – as the basis for future policymaking. The study’s predictions of the impacts on fisheries, agriculture and the economy across the basin if hydropower projects go through are dire – and for Cambodia, they are potentially catastrophic.

The Council Study, a 3,600-page report that was six years and millions of dollars in the making, was commissioned by MRC countries to assess in particular the 11 proposed dams along the lower Mekong mainstream, of which three are already under construction.

“Certainly the results show that if the business as usual trajectory plays out that the trade-offs to water and food impacts are going to be very dire,” said Brian Eyler of the think tank The Stimson Center.

“We’re looking at a zero-sum gain or a negative sum gain for the region,” he continued, adding “China’s leadership needs to pay attention to this, as does the leadership downstream”. Though China is not in the MRC, it attended the summit as a “dialogue partner” along with Myanmar.

Danger of invasive species

MRC Chief Environment Management Officer So Nam said conclusions about fish loss in the study are not only consistent with those produced by other research, but have been subjected to the scrutiny of international experts. They find that if alterations made to dams are 50 percent effective in allowing for fish passage, fish biomass in the Cambodian Mekong would still drop by one fifth by 2020 and 35 percent by 2040.

Not only would there be a reduction in fish numbers, but also drastic changes in fish types – with migratory “white fish” species predicted to disappear entirely from Thailand and Laos and being pushed to the brink in Cambodia. Taking their place in large part are invasive species, which put pressure on the natural ecosystems and whose emergence, So Nam said, is nearly irreversible.

“It’s really a frightening situation, not only from the dams but also from another human activity of stopping this introduced species,” he said.

The study also predicts that the economic benefits of hydropower would not make up for the decline of fisheries, with Nguyen Thi Ngoc Minh, a specialist at the MRC, forecasting a 20 percent reduction in the country’s projected GDP by 2040.

For the fishermen and farmers that depend on the river system for their food and livelihood the prospects aren’t good.

“There really could be a food security and a public health crisis that comes out of this,” said Maureen Harris of International Rivers.

“It’s also explicit [from the study] that the losses or the threats are being felt most by poor and vulnerable communities within the basin and that the impacts will be exacerbated on these populations through climate change as well,” she said.

One key finding was that mainstream dams, if built without mitigation mechanisms, would reduce sediment flow to the delta, which includes Cambodia and Vietnam, by 67 percent by 2020, and a whopping 97 percent by 2040 – a figure water security expert David Grey called “a deal-breaker” during a panel discussion.

Sopheap Lim, a modeller with the MRC, said such reductions would impact rice production, as well as fish and floodplain productivity, while also causing riverbank erosion. The MRC predicts $6.7 billion would be needed for riverbank reinforcements between Vientiane and the delta to offset the effects.

“This really questions the viability of the delta going forward and any sustainable possible ongoing agriculture and livelihood support in the delta, so it’s really quite catastrophic in terms of what this could mean,” said Harris.

Even with mitigations – changes to the design of dams to allow more sediment to pass – the amount reaching downstream floodplains would still be quite low, according to the study.

‘It’s not a river anymore’

The message to leaders at the end of Tuesday called on the need for investments that “sustain water-food-energy-environment security”, establish and maintain protected areas in the Mekong and consider alternative energy sources.

“We need to be careful, and make use of the results and further work together,” said Te Navuth, Secretary General of the Cambodia National Mekong Committee.

“Of course a serious impact will be [felt] to the downstream, Cambodian Mekong Delta, Vietnam Mekong Delta, Tonle Sap River system, fisheries, water regime, sediment,” he said.

Youk Senglong, the deputy executive director of the Fisheries Action Coalition Team (FACT), said the study only adds to a host of scientific literature that should be considered.

The changes to the river will be such that “it’s not a river anymore”, Senglong said.

“We’re afraid … because there is a close connection between the Tonle Sap great lake, which is the heart of Cambodia, and also the Mekong.”

He implored Prime Minister Hun Sen and the other Mekong leaders to carefully and fully address the findings of the Council Study in making their decisions.

A joint statement to the MRC country leaders on Wednesday from 10 countries – including Australia, the United States, Japan and Sweden – and the European Union, World Bank and International Union for the Conservation of Nature, expressed concern about the study’s findings. It described the report as a “sound and neutral basis” for understanding the trade-offs of hydropower development.

“Given the severity of the projected impacts of planned and ongoing investments on fisheries, food security, health and livelihoods, as well as the region’s commitment to the Sustainable Devleopment Goals, we look forward to seeing how the Member Countries translate the findings of their Council Study into policies,” the statement reads, going on to encourage member countries to “revisit their development models”.

Country delegations also released statements on Wednesday, with only Thailand and Vietnam making note of the Council Study. Cambodia did acknowledge that food, energy and water security challenges faced are “more serious than before”, while Laos reaffirmed that its hydropower development projects, which make up 9 of 11 total projects on the mainstream, “followed the MRC procedures”.

China, which has built six dams on the Mekong in its own territory and is a major financer of hydropower development downstream said it “understand[s] and respect[s] the reasonable concern of the Mekong countries on hydropower development”.

A statement from Dr Tran Hong Ha, Vietnam’s Resources and Environment Minister, explicitly called on regional governments to heed the study and said “the sustainability of development of Mekong Basin and riparian countries, and even their existence”, depends on cooperative transboundary water management.