Representatives for Cambodia, Laos, Thailand and Vietnam meeting in Sihanoukville deferred a decision on a controversial hydropower dam on the lower Mekong river in Laos, according to a statement issued by the Mekong River Commission over the weekend.

The four countries will meet again on April 21 in Vientiane, while a deadline for the decision is set for April 22.

The four countries also released a review by the MRC of documents related to the proposal.

“The gaps in knowledge on the number of migratory fish species, their biomass and their ability to successfully pass a dam and reservoir leads to considerable uncertainty about the scale of impact on fisheries and associated livelihoods, both locally and in a transboundary context,” the report concluded.

The report estimated that a full 2.5 million tonnes per year, or six percent of fishery yields, would be lost.

Ame Trandem, Mekong campaigner for International Rivers, said that the MRC’s assessment of the dam’s uncertainty demonstrated it should be shelved.

“It’s quite clear from the significant array of knowledge gaps that remain and from the risks the project poses, that the ... project should be cancelled, she said.”