“The sediment was full of gold, I used to find pieces the size of a tamarind seed,” she said, hacking into the river bank with a pickaxe and removing clumps of mud and stone.

“Since the dams were built the river water rises and falls randomly and the ecosystem is off balance, we have to pan on the edge of the river where there are only tiny amounts of gold.”

US claims China’s ‘manipulation’ of Mekong is ‘urgent challenge’

On a lucky day Rodjana and her childhood friend Hieng Chantarasee, 70, can make 500 baht (US$15) from collecting flecks of gold that can be fashioned into one thumbnail size piece.

Activists say the protein-laden fish diets, livelihoods and environment of those millions have been put in jeopardy as mainly Chinese, Thai and Vietnamese companies tap the river for hydroelectric power.

“I realised things were changing when the fish died and the water rose suddenly,” said Hieng, sitting on a foot-high plastic stool semi-submerged in the water.

But Rodjana and Hieng feel sure the dams are to blame for the deteriorating health of a river that has been their families’ playground and source of food and income for generations.

“It’s distressing. But what can we do?” Rodjana said. “All we ask is please don’t build any more dams.”

But it is a forlorn hope.

A new dam is already planned 2km upstream from their panning site in Laos.

The Sanakham is a US$2 billion scheme developed by a subsidiary of China’s Datang International Power Generation Company. Construction was set to begin late last year and finish in 2028, according to the Mekong River Commission, with the power generated to be exported mainly to Thailand.

Of the US$2 billion price tag, only around US$28 million (or 1.4 per cent) has been set aside for environmental and social mitigation measures, according to the commission, a forum for Laos, Cambodia, Thailand and Vietnam to discuss their water worries.

Thailand is slowly turning against the dams, with river communities lobbying for a pause in development and officials beginning to openly debate the need for the electricity generated by hydropower and set to be sold to the kingdom.

“The development of the Mekong has reached the point of no return,” said Tosapol Wongwan, assistant to the Secretary General, Thailand’s Office of the National Water Resources.

“All we can really do right now is to focus on how we can reduce the impact which will probably take at least 15 years.”

Gradually, upstream countries – China and Laos – have begun sharing data on water flows and forewarning of dam closures and release to the downstream neighbours.

But full transparency is hard to achieve between countries with competing strategic, economic and national security demands.

Satellites to track Chinese dams on Mekong, as US likens ‘threat’ to South China Sea

Laos holds the key. Poor and landlocked, the country’s communist government is seeking to become the “Battery of Asia” using its dominant share of the Mekong.

It has two dams in operation – the Thai-developed Xayaburi in the north and Don Sahong near the Cambodia border. But there are another seven planned for the Laos stretch of the Mekong and many more on its tributaries.

Critics say there is little oversight of deals with Laos’ authoritarian government, or transparent assessments of the need for, or environmental impact of, the dams.

China, which is driving the dam-building spree, insists hydropower is an environmentally friendly resource to drive the economies of the Mekong, and says claims to the contrary are groundless and politicised.

But as the dam-building continues the forecast for the river is ominous, according to Songrit Kirk Pongern, a Mekong researcher and academic at Thailand’s Kasetsart University.

“In five years’ time the impact will be seen more clearly,” he said. “The fish population will continue to decline; downstream will be starved of sediment, riparian and local fishing will vanish and food security for 60 million people will be depleted.”