Environmentalists have criticised Laos for pressing ahead with plans for another "destructive dam" on the Mekong River, a waterway already strangled by hydropower schemes.

The flow of the Mekong, Southeast Asia's longest river, is interrupted by a cascade of dams in China -- where it is called the Lancang.

Water levels have dropped to record lows over the last year, exposing rocks and killing fish, a phenomenon blamed by villagers in Thailand and Laos on the operations of dams.

On Monday, Laos' communist government submitted proposals for the Sanakham dam -- close to the northeastern border with Thailand -- to the Mekong River Commission (MRC).

The MRC is a dam consultation body for Mekong nations, but has been accused of being toothless in stopping river projects sponsored by governments and big business.

The consultation process is in fact a "rubber stamp" to get work started on the Sanakham this year in time for a 2028 completion, according to International Rivers, a key campaign group against damming.

Laos' communist government has submitted proposals for the Sanakham dam -- close to the northeastern border with Thailand -- to a consultation commission Laos' communist government has submitted proposals for the Sanakham dam -- close to the northeastern border with Thailand -- to a consultation commission Photo: AFP / Lillian SUWANRUMPHA

"What the Mekong needs immediately is the moratorium on large-scale hydropower dams... not more destructive dams that will benefit a few at the expense of communities in the Mekong basin," Paiporn Deetes of International Rivers told AFP.

The MRC says the Sanakham dam consultation includes an environmental impact assessment on the waterway and its communities.

Landlocked, corrupt and poor, Laos has turned to billion-dollar hydropower schemes for investment, hoping to sell the electricity for a profit to its neighbours as well as provide energy to its remote populations.

But critics say dams have been railroaded through despite mounting evidence of ecological damage to one of the world's most biodiverse waterways.

Villagers along the Mekong in Laos and Thailand say their fish catch has dwindled as the dams have come online.

Studies show sediment flow has thinned, leaving the river increasingly anaemic as it winds towards the Vietnamese delta.

The Mekong feeds around 60 million people.