The wall would run 10,844 metres - nearly eleven kilometres of structure stretched bank to bank across the Mekong - and stand just 22 metres high, about the height of a seven-storey building. That ratio tells you what kind of dam this is. The Stung Treng project is not a canyon plug wedged into a narrow gorge; it is a low barrier laid across a river so wide and so flat that the only way to hold it is to build sideways. Nineteen years after the first feasibility study was licensed, not a single cubic metre of it has been poured.
In 2007 the Russian firm Bureyagesstroy, a subsidiary of RusHydro, obtained a licence to study the site. The study was carried out, the company asked for permission to build, and trade press at the time described a roughly two-billion-dollar, 960-megawatt proposal. Then the file moved. On 9 December 2009 Cambodia signed a memorandum of understanding with IDICO, a Vietnamese state investment corporation, for an entirely new feasibility study. The results of that survey have never been released.
March 2020 brought the sharpest turn. Citing ecological concerns, the Cambodian government suspended all hydropower development on the Mekong mainstream until 2030, shelving Stung Treng along with its far larger downstream neighbour, the proposed 2,600-megawatt Sambor Dam. The moratorium did not quite close the matter. In 2022 the Royal Group, one of Cambodia's largest conglomerates, obtained permission from the Ministry of Mines and Energy to run feasibility studies at three candidate sites - inside a ban, for a dam that cannot legally open before 2030.
On paper the numbers are attractive. Ten turbines of 98 megawatts each, 980 megawatts installed, roughly 4,870 gigawatt-hours a year for a country that has never had enough electricity. Behind the generating hall would sit a reservoir covering 211 square kilometres and reaching some 50 kilometres upriver - far enough to back water toward the provincial capital itself.
The counter-argument is written in fish. The lower Mekong basin holds an estimated 850 freshwater fish species and yields around 4.5 million tonnes of fish and aquatic products a year, worth somewhere between 3.9 and 7 billion dollars. Roughly 40 million rural people take their living from it. In Cambodia the dependence is starker still: about 80 percent of the population's annual protein intake comes from the Mekong system. A 2012 study by the Inland Fisheries Research and Development Institute concluded that the Stung Treng dam alone would cut yields of fish and other aquatic animals by between 6 and 24 percent, and that the migration routes feeding the Tonle Sap - the largest inland fishery on Earth - would be essentially wholly blocked.
The reach immediately upstream of the dam site is not ordinary river. On 23 June 1999 Cambodia designated the middle stretches of the Mekong north of Stung Treng as a Wetland of International Importance under the Ramsar Convention: 14,600 hectares of braided channels, rapids, seasonally flooded forest and deep dry-season pools where fish shelter when the water drops. Signing that convention committed the government to three things - to conserve the wetlands it has listed, to weigh wetland use in national planning as far as possible, and to consult its neighbours about transboundary wetlands, shared water systems and shared species.
Those neighbours have standing here for a second reason. As a member of the Mekong River Commission, Cambodia must give prior notification of any hydropower built on the mainstream, which puts a Stung Treng design in front of Laos, Thailand and Vietnam before it puts it in front of a contractor. A commission-authorised report released in January 2010 recommended that Stung Treng and Sambor both be deferred for ten years. That ten-year pause expired in 2020 - the same year the government imposed one of its own, running to 2030.
Anyone wondering what Stung Treng would actually mean can look 25 kilometres up the Sesan River from the provincial capital, where the Lower Se San 2 Dam entered full operation on 18 December 2018. It is a far smaller machine - 400 megawatts from five turbines - and it sits on a tributary rather than the mainstream.
Its consequences were not small. Up to 2,000 people were displaced by the reservoir. Impact assessments found that at least 38,675 people in no fewer than 86 villages along the Sesan and Srepok rivers, a great many of them from indigenous communities, would lose access to the bulk of their fisheries once the dam severed migration from the Mekong and Sekong, and that roughly 78,000 people living above the dam site would lose migratory fish altogether. These were households whose year was organised around when the fish arrived, on reaches their grandparents had fished, and no compensation schedule reproduces that.
The Stung Treng dam would run the same arithmetic on the mainstream itself. That is why, nineteen years on, it remains a drawing.
The proposed Stung Treng Dam site lies at 13.0587 N, 105.983 E, on the Mekong mainstream roughly 50 km downstream (south) of Stung Treng town in north-eastern Cambodia. Nothing is built here, so there is no structure to look for - what you see instead is the reason the site was chosen: a broad, braided, island-strewn reach where the Mekong runs wide and shallow across a nearly level floodplain. In the dry season, from roughly December to May, sandbars and rock shelves stand exposed and the channel splits into a maze of threads; in flood the whole width runs as one sheet. Recommended viewing altitude 3,000-6,000 ft AGL to take in the full 10.8 km bank-to-bank span that any dam here would have to cross. The Ramsar wetland reach begins north of Stung Treng town and runs up toward the Laos border. Nearest operating airport is Techo International at Phnom Penh (VDTI), roughly 320 km south-west; the provincial airstrips at Stung Treng, Kratie and Ratanakiri are abandoned and unserviced. Expect dry-season haze February to April and vigorous afternoon convection over the river corridor from May to October.