The once mighty Mekong river has been reduced to a thin, grubby neck of water in stretches of northern Thailand -- record lows blamed on drought and a recently opened dam far upstream.

The $4.47 billion Thai-owned Xayaburi dam went into operation this week in Laos after years of warnings over the potential impact on fish flow, sediment and water levels of a river which feeds millions.

Experts say the Mekong river is at a "crisis point"
Experts say the Mekong river is at a "crisis point" AFP / Lillian SUWANRUMPHA

Along parts of Thailand's northeastern border at Loei, the kilometre (3,300-foot) wide river has shrivelled to a few dozen metres, with boulders and bedrock encasing muddy pools of water.

From above the encroaching banks of Laos and Thailand are now a thread of water apart, restricting fishing grounds to a slim channel.

Along parts of the northeastern Thai border, the river has shrivelled to a few dozen metres in width
Along parts of the northeastern Thai border, the river has shrivelled to a few dozen metres in width AFP / Lillian SUWANRUMPHA

Fishermen blame a combination of this year's weak monsoon and the Xayaburi dam, around 300 kilometres (185 miles) to the north.

"I don't want any more dam construction," said fisherman Sup Aunkaew, who tossed a meagre catch into his boat, adding that the fish spawning habits have been "confused" by the unseasonally low water levels.

The Mekong sustains tens of millions of people along its banks through fishing and agriculture
The Mekong sustains tens of millions of people along its banks through fishing and agriculture AFP / Lillian SUWANRUMPHA

"But we can't really oppose their plans if they want to do it."

Landlocked and impoverished Laos has set its sights on becoming "the battery of Asia", with 44 operating hydro plants and 46 more under construction many on key tributaries of the Mekong, according to monitor International Rivers.

Experts say the dam-building frenzy in China and Laos has compounded the drought
Experts say the dam-building frenzy in China and Laos has compounded the drought AFP / Lillian SUWANRUMPHA

'Death of a thousand cuts'

Experts say the dam-building frenzy in China and Laos has compounded the drought.

"These are causing the Mekong to die a death of a thousand cuts," said Brian Eyler, author of "The Last Days of the Mighty Mekong."

"Some parts of the river (have) hit historic lows for any time of the year."

He said the lower part of the river is at a "crisis point" until rains come again next year but no one is sounding the alarm.

The Mekong, which rises on the Tibetan plateau and courses through China, Myanmar, Laos, Thailand, Cambodia and Vietnam -- sustains tens of millions of people along its banks through fishing and agriculture.

The 1,285-megawatt Xayaburi dam was built by CKPower -- a subsidiary of the Thai builder and majority shareholder CH Karnchang -- which went ahead with construction despite protests in Thailand, which is buying most of the electricity.

As it began operations the company plastered Thai newspapers with advertising this week referring to the "greatness of the Mekong" and calling the dam "fish friendly".

It did not immediately respond to requests for comment but trumpets its commitment to clean, sustainable energy.

In July the dam operator denied tests on the mega-structure were responsible for the river to dry up downstream in northeastern Thailand.

China Thailand