Myanmar and Thailand have begun building a controversial hydro-power dam on the Salween River, the as yet longest undammed waterway in Southeast Asia, official media reported Thursday.

Thailand’s MDX Group Co Ltd has invested about six billion dollars in the Tasang project in eastern Shan State, which is the biggest of four planned dams on the Salween.

The state-run New Light of Myanmar newspaper said construction began on March 30 — a move likely to dismay environmentalists who had called for a delay to allow a public consultation on the project.

Activists say the dams could prove disastrous to Salween’s delicate ecosystem and accuse Myanmar’s military junta of using the dams as an excuse to evict thousands of ethnic minority villagers from their land.

The New Light of Myanmar said the dam located about 45 miles (75 kilometres) from the Thai border in Myanmar’s Shan state would be 2,848 feet (868 metres) long and 746 feet (227 meters) high.

“On completion, generators to be equipped at the power station will have a total capacity of 7,110 megawatts and the project is expected to produce 35,446 million (kilo-watts per hour) yearly,” the newspaper said.

Senior officials from Myanmar’s state-run energy firms and MDX Group attended an official opening ceremony.

Three more dams on the Salween near the Thai-Myanmar border are in the pipeline, mostly backed by Chinese state-owned energy companies.

The United States and Europe have economic sanctions against military-run Myanmar to punish them for the ongoing detention of democracy leader Aung San Suu Kyi and other human rights abuses.

But energy-hungry neighbours like Thailand, China and India are keen to exploit the country’s abundant natural resources including energy, natural gas and timber, throwing an economic lifeline to the military junta.