For opponents of the Don Sahong dam project, any opportunity to halt the project hinges on the wording of the agreement that set up the Mekong River Commission (MRC).
A year after Laos began construction on the Xayaburi hydro dam, despite alarm over fish migration and sediment flows, the Don Sahong project is raising similar fears.
To combat what they see as a new threat, environmentalists are turning to the MRC, set up in 1995 to help Cambodia, Laos, Thailand and Vietnam jointly manage and develop the Mekong River.
The key issue now is whether Laos has breached the MRC agreement, under which members must be consulted before any dam is built along the mainstream.
For Don Sahong, the Laotian government used the channel of prior notification on Sept 30, a process not requiring all MRC members' opinions, claiming the dam is outside the mainstream.
But environmentalists argue an environmental impact assessment (EIA) conducted before 2007 and reviewed by the MRC defines the project as a mainstream dam.
Pianporn Deetes, International Rivers' Thailand campaign coordinator, said Laos failed to consult in reaching its conclusion that Don Sahong is outside the mainstream and that its engineering meets MRC guidelines.
In her view, this sets a dangerous precedent.
Besides, the Laotian government only released the project's EIA to neighbouring countries and the public only days before construction was due to begin, she added.So far, 41 projects on Mekong tributaries have been submitted for notification. But Xayaburi is the only project proposed on the mainstream and therefore submitted for prior consultation.
Surasak Glahan, spokesperson of the MRC secretariat, told the Bangkok Post that none of its four member countries has suggested holding further discussions on Don Sahong.
If a request were made, the project would undergo consultation, delaying construction by six months.
While the MRC has been criticised as ineffective, Mr Surasak said the commission was set up to develop projects with minimal impact, not to conserve the environment.
"The MRC is not a magic pill that can satisfy everyone, but at least it fosters cooperation up to a certain point and helps reduce conflicts," he said.
Neighbouring countries have a right to request compensation if a project has a significant impact and the last resort is international arbitration, although that has yet to happen.
Meanwhile, 103 civil society groups handed a letter to the Ministry of Natural Resources and Environment on Monday asking for help in halting the project.
Montree Chantawong, a water expert of the Towards Ecological Recovery and Regional Alliance, said the Thai government should ask Laos to switch the project from "prior notification" to "prior consultation".
"The MRC has agreed that Don Sahong is located on the mainstream Mekong as appeared ubiquitously on its documents," he said.
"Laos' claim that this project is on a tributary is incorrect. The other three lower Mekong countries must be informed and consulted."