Laos' work on the Mekong river draws criticism
4 July 2012 Last updated at 04:03 BST
In a dusty gorge deep in landlocked Laos, work is underway on a project that could change South-East Asia forever.
Despite the protests of countries downstream and the warnings of scientists, a construction company has begun building the first dam across the lower reaches of one of the world's great rivers.
Officially the Lao government says it has not decided whether to go ahead with damming the Mekong at Xayaburi - but all the evidence suggests otherwise.
Jonah Fisher reports.