It runs 1,900 miles (3,060 kilometres) from the high Tibetan mountains to the Gulf of Martaban, and along its great length there are few places more remarkable than Weigyi, on the border of Burma and Thailand.

Here the god of the Salween shows himself in the form of a notorious whirlpool that churns the waters and can even drag a boat under. Locals leave offerings of rice, flowers and bananas to appease the deity and to thank him for the prosperity he brings.

But now ominous signs have appeared, signs that promise disaster for the people of the Salween and their god.

They come in the form of yellow marks painted on the rocky banks and a concrete plaque laid by Thai engineers. If their plans go ahead Weigyi will be transformed from a jungle shrine into a massive hydroelectric dam.

The rocky cliffs will be replaced by concrete walls and throbbing turbines. The jungle will be penetrated by rumbling roads and high security fences.

Five dams are jointly planned by the Thai and Burmese Governments; far upstream China proposes building 13 more. If only a few go ahead, the Salween, the longest undammed river left in south-east Asia, will be chained.

Conscious of the potential for bad publicity, the Thai and Burmese Governments have kept secret their precise plans for dam building. But The Times has obtained a copy of the memorandum of agreement signed between them last December.

It reveals that the first dam to be built will be at Hatgyi, south of Weigyi. This is an area firmly under Burmese control and 30 miles inside its territory. The guerrillas of the Karen National Union and independent observers will find it very difficult to observe its effect on local people. Construction is due to begin late next year.

“As long as I have lived here my family has been totally dependent on the Salween for our livelihood,” says Htoo Lwee, a member of the Karen ethnic group that lives in the village of Hoekey, a few miles below the proposed dam site at Weigyi. “The river gives us a living from fishing and from boating. It is our life and our mother. If the dam is constructed we will not be able to live.”

The Salween is home to 70 species of fish including catfish, eel, featherback and carp who thrive in its surging rapids and deep pools. The dam would create a still-water lake to which they are ill-adapted.

The dam’s opponents calculate that the reservoir will be 640 sq km — the size of Singapore.

It will destroy rice paddies, vegetable fields, 26 villages and two entire towns. Temples and palaces will be submerged; 22,000 people will lose their homes and 8,000 more will lose their livelihoods.

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