By Alex Kirby
BBC News Online environment correspondent in Dushanbe, Tajikistan
An ambitious plan to try to restore to health part of the shrinking Aral Sea has been mounted by Kazakhstan.
The sea's retreat spells disaster for local people
It involves building a massive dam to separate for ever the two distinct parts into which the sea has now split.
But the project has a serious downside: if it succeeds, it means the virtual abandonment of any hope of restoring the sea's far bigger southern section.
The Aral, once the world's fourth biggest inland sea, has halved in depth and lost 90% of its volume in 40 years.
Kazakhstan and its neighbour Uzbekistan share the Aral's waters. With Turkmenistan, Kyrgyzstan and Tajikistan, they have formed the International Fund for Saving the Aral Sea (Ifas).
Sirodjidin Aslov, who chairs the Ifas executive committee, gave details of the Kazakh project at the fund's headquarters here.
The dam, which will replace an earlier mud-built version that collapsed last year, will be a concrete structure 12.7 kilometres (eight miles) long.
It is being built to complete the barrier between the northern and southern parts of the sea formed by an island exposed by the falling waters.
The dam should raise the water level to between 38 and 42 metres, a level not seen for more than a decade. The Kazakhs hope to finish work in about four years' time.
Mr Aslov, a Tajik citizen, said: "In eight or 10 years we hope the northern shoreline will have returned to where it used to be. The dam is a very good idea, because it will restore the Kazakh fishing industry."
He painted a grim picture of the entire sea's decline, from a volume of about 1,000 cubic km 40 years ago to 110 today.
More efficient irrigation technologies are needed
The water level fell in that time from 53 metres to 28, and the shoreline receded by up to 250 km (155 miles).
The annual inflow in 1960 was 63-65 cu km, he said, but now it was about 1.5. Yet 10 cu km were needed just to keep the sea as it was, let alone to reverse its plight.
The situation of the southern part of the sea he described as "disastrous".
One foreign expert told BBC News Online: "Forget the southern Aral Sea. When the dam is built, it will get scarcely any water. But it's gone already - it's lost."
Mr Aslov said the mineral content of the water was now up to seven times higher than 40 years ago, with pesticides and fertilisers combining with salt to produce "a sort of salty paste".
The devastation of the Aral Sea, which has been called "the worst man-made ecological disaster on the planet", dates from the Soviet era, when huge tracts of central Asia were turned over to chemically intensive cotton farming.
Mr Aslov said: "The impact of those days is disastrous, and most of all on people's health.
"In the areas nearest the sea anaemia, cancers, liver and kidney diseases and children's illnesses are all increasing. The Soviets turned the Aral Sea into trash."
Inefficient irrigation systems still consume huge amounts of water which would once have reached the sea.
The Syr Darya, which flows into the northern section through Kazakhstan, provides almost all the inflow to the entire Aral. The more southerly Amu Darya contributes little more than a trickle.
A sixth country, Afghanistan, is now planning to join Ifas. Mr Aslov said up to 10% of the Amu Darya's flow came from Afghanistan, so it had every right to be involved.
The Aral is paying the price of damaging Soviet policies
He said a regional approach was the only possible way to save even part of the sea.
A British Embassy official here, speaking in a personal capacity, said: "I see no serious prospect of military conflict in central Asia over water in the next 10 years.
"But unless the situation changes, I shouldn't like to commit myself beyond that."