The possibility, indeed probability, that Laos will build its controversial 32m-high dam at Don Sahong on the Mekong River just above the Lao-Cambodia border has strengthened following the Mekong River Commission (MRC) Council meeting in Bangkok on 26-27 June. This is despite an apparent concession by the Lao delegation, with Vice-Minister for Energy and Mines Viraphonh Viravong agreeing to six months of 'consultation' with the other MRC members (Cambodia, Thailand and Laos) over the dam's construction.

In making this concession, Laos has shown some readiness to acknowledge criticism of the planned dam, which has come principally from Cambodia and Vietnam (Thailand has been much less forceful). There will now be a formal exchange of ideas and plans relating to the proposed dam.

But as MRC chief Hans Guttman said after the meeting, 'Under the MRC's regulations there is no need to suspend or stop work on the project during the (consulation) process.'

The Lao Government, and Viraphonh Viravong in particular, has shown itself adept at gaming the rules and regulations stemming from the 1995 Mekong River Agreement. In the case of the Xayaburi dam, which has now advanced to actual construction, Laos blindsided fellow MRC members by simply ignoring until the last moment the requirement for consultation, and then announcing that the dam was under construction.

With Don Sahong, the Lao Government adopted another approach, claiming the dam was being built on a 'tributary' of the Mekong rather than the mainstream and that, under the agreement, this meant it only had to give a notification of its intentions. At the very least this was a terminological sleight of hand. The site of the planned dam at Don Sahong is on one of the many channels into which the Mekong splits when it reaches the region of the Khone Falls (pictured). Until last year it had never been suggested that the dam site on the Hou Sahong Channel was other than part of the river's mainstream.

So the Lao concession in Bangkok seems very much like a fig leaf for the Government's ultimate intention to build the dam; work has already begun on preliminary construction such as housing and bridges. The plan was always to begin work on the Hou Sahong Channel itself in December 2014, so consulting for six months would only delay those plans for a month.

The Lao Government and the Malaysian firm contracted to build the dam have repeatedly argued that means will be found to mitigate the effect of blocking the Hou Sahong Channel, which is the only route through which large numbers of fish are able to migrate throughout the year. The Government and builders claim this will be possible by improving the morphology of other channels.

The science bearing on this issue appears beyond dispute: only Hou Sahong offers year-round migration. For this channel to be blocked threatens major disruption of fish stocks both below and above the Khone Falls. There is an abundance of scientific literature on the issue, with this World Fish Center summary the most easily available. A more recent article in Nature expands on the damage likely to flow from construction of a dam at Don Sahong.

The Lao Government understandably wants to improve its foreign exchange earnings by embracing hydropower generation, which is why Xayaburi is being built and why it wants to build Don Sahong. But the costs, including to Laos itself in terms of lost fish stocks, is high. Even if there is an argument to be made that the dam at Xayaburi will have a relatively limited effect on the overall fish catch, this is not the case for Don Sahong.

Photo by Flickr user Global Water Forum.