Despite opposition from neighbouring countries and environmentalists, the government of Laos has given approval for full construction work on a dam on the lower Mekong River.
The government said a formal ceremony marking the start of full construction at Xayaburi would be held on Wednesday.
Deputy energy minister Viraphonh Virawong said work on the Xayaburi dam itself would begin this week, and he hoped it would be the first of many.
A BBC correspondent says the $US3.5 billion dam is being built by a Thai company with Thai money - and almost all of the electricity has been pre-sold to Thailand.
Four dams already exist in the narrow gorges of the Upper Mekong in China, but until now there are none on the slower moving lower reaches of the river.
Mr Viraphonh said he believed that concerns about fish migration and sediment flow had been addressed due to modifications to the original dam design costing more than $US100 million.
Sediment will be allowed out of the bottom of the dam periodically through a flap and lifts, and ladders will help the fish travel upstream.