They threatened aggressive campaigns against governments and financial institutions which support the schemes.
Itthipol Kamsuk, a coordinator of the Northeast Community Network of the Mekong River Basin (ComNet Mekong), said the people living along the Mekong are suffering from dam project impacts.
They feared the situation would get worse if a number of hydropower dam projects, especially in Laos, are allowed to continue.
The Lao government has approved the construction of the Xayaburi dam and about 21% of the project has been completed. It also notified member countries of the Mekong River Region in September last year it would construct a 256-megawatt hydropower dam at Hou Sahong in Champasat province amid concerns over the possible environmental and fishery impacts on neighbouring countries.
"All governments should respect locals' voices opposing the projects as the impacts on them are quite clear. The governments must put all their efforts into stopping the hydropower dam projects in the Mekong River," he said.
All Thai banks must stop supporting the Xayaburi dam project, Mr Itthipol told a regional public forum on the Don Sahong dam project in Laos. He said his network will launch a campaign to urge depositors to withdraw money from Bangkok Bank, Krung Thai Bank, Siam Commercial Bank and Kasikornbank as these banks granted financial support to the dam projects.
Ormboon Thipsuna, a member of ComNet Mekong, said the impacts of the dams could be clearly seen from less fish caught in the river. The project also affected farms along the Mekong and the tourism industry. If all the governments ignored their peoples’ voices, the group would campaign for the closure of bridges over the Mekong River linking Thailand and Laos, he said.
Lan Thi Thu Suu, a coordinator of the Vietnam Rivers Network, said hydropower dams have affected the ecology of the Vietnamese delta, the country’s main rice growing area.
"It is important to put more pressure on the governments to try to make them comply with the 1995 Mekong Agreement to protect and preserve the international river," she said.
Youk Senglong, programme manager of the Fisheries Action Coalition Team, said scientific records have shown the six dams on the upper Mekong River in China have adversely affected the people living downstream.