Over 11,000 people from the six countries of the Mekong River region have signed a petition addressed to the Prime Ministers of Cambodia, Laos, Thailand and Vietnam, seeking to prevent the building of a dam.
A further 5,000 people from countries around the world also sent in postcards or signed an online petition to save the river which is a source of food for some 60 million people.
Mekong Programme Coordinator Carl Middleton said that due to the overwhelming response, regional governments would reconsider the plan and were expected to make decisions in favour of saving the life and environment of their own countries.
Since 2006, eleven hydropower dams have been proposed at different locations along the Mekong.