Finally, after months of equivocation, the Lao Minister for Energy and Mining, Viraphon Viravong, announced on 5 November that the Vientiane government will proceed with its plans to build the controversial dam at Xayaburi (pictured), roughly midway between Luang Prabang and Vientiane. A ceremony to mark this decision will take place tomorrow.

It's hard not to read something into the date chosen for this announcement: to give a public airing to a controversial issue when attention in Vientiane is focused on the Asia Europe Meeting summit. More importantly, this decision finally breaks the decades-old consensus that building dams on the mainstream of the Mekong after it flows out of China poses such dangers to the environment that no action should be taken until a thorough environmental assessment has been made.

The Lao authorities maintain that the dam will not have serious effects for downstream neighbours Cambodia and Vietnam. This is a position those two countries have until now sharply rejected, fearing the effects of the dam on fish stocks and on the flow of sediment down the river. For the moment, the governments in Phnom Penh and Hanoi have not reacted to the announcement.

There has long been a concern that once one dam has been built it will be difficult to prevent others being constructed. If this were to take place, the majority would be constructed in Laos, but Cambodia also has prospective sites for dams on its section of the Mekong.

If nothing else, the Lao decision has shown the extent to which the Mekong River Commission can only ever be a consultative body and underlines its lack of mandatory authority so far as the actions of its members are concerned. And the decision underlines the extent to which self-interest has clearly trumped the shared ASEAN identity of Laos, Cambodia and Vietnam.

Photo by Flickr user International Rivers.