The MRC's donors, which include the World Bank, the United States, Japan, Australia and many European governments, are due to meet in the Cambodian town of Siem Reap today.

The Bangkok-based Terra (Towards Ecological Recovery and Regional Alliance) has warned that the dams, set to come up on the lower part of the Mekong, will displace up to 75,000 people and threaten the food security of millions more.

The projects will also endanger up to 1,300 aquatic species including the rare Mekong giant catfish and the Irrawaddy dolphin.

The group said the MRC - which comprises Cambodia, Laos, Thailand and Vietnam - has failed since its creation in 1995 to carry out adequate environmental impact assessments or consult those people affected by the dams.

Terra also wants the donors to pressure the MRC to make sure people are compensated for any loss of livelihood.

Around 60 million people in six countries - Cambodia, China, Laos, Myanmar, Thailand and Vietnam - depend directly or indirectly on the Mekong River basin's resources.

The six dam projects will together generate 9,645MW of electricity, much of which will be bought by Thailand.

But one of the proposed dams - the Sambor dam in Cambodia's Kratie province - will block a critical migratory passage for fish moving upstream from the giant Tonle Sap lake. This will affect the Cambodian fisheries industry, which provides roughly 12 per cent of the country's gross domestic product (GDP).

The environmentalists say dams across the upper reaches of the Mekong in China have already triggered a 50 per cent drop in the fish catch downstream in Thailand's Chiang Rai province, forcing many fishermen to seek jobs in the cities.

But that view was challenged by MRC chief executive officer Oliver Cogels last December, who said the downstream effects of dams in China was often exaggerated.

He said the dams may instead increase the availability of water in the dry season.

Meanwhile, Ms Pianporn Deetes of the Living Rivers Siam organisation has told reporters: 'When we visit dam-affected areas, we find the public have not been informed about the dams or been allowed to participate meaningfully (in any decision-making processes).'

And Professor Surichai Wungaeo, director of Chulalongkorn University's Social Research Institute and a member of Thailand's National Legislative Assembly, said the MRC 'needs to be more responsive to civil society voices - not just the riparian governments'.

nirmal@sph.com.sg