The gradual drying up of the Aral Sea has left a toxic wasteland threatening some three million local residents and "will cause climate change over a vast territory", Rakhmonov said.

Clouds of pesticide-laden salt continue to be blown into the surrounding region, the central Asian republics of Kazkhstan and Uzbekistan.

Rakhmonov also focused on the water crisis in his own country Tajikistan, which lies southeast of Uzbekistan, and borders Afghanistan.

"It has become quite evident that either single-handedly or with the support of all Central Asian states, Tajikistan will not be able to deal with the threat of a humanitarian and ecological disaster," he warned.

But critics doubt Central Asian leaders' commitment to cooperating on the water issue.

Delegates from some 50 states around the world gathered for the keynote gathering here on the world water crisis in the "year of fresh water," declared by the United Nations at Tajikistan's initiative.

"Today more than one billion people the world over lack access to safe drinking water," Rakhmonov told delegates from around 50 countries.

"All over the world both the quantity and quality of safe water are decreasing as a result of pollution, over-consumption and mismanagement," UN Secretary General Kofi Annan said in a written message to the conference:

"Each year more than two million children die from water-borne diseases."

The source of much of Central Asia's water, Tajikistan's own complex network of dams and rivers has been severely degraded by years of neglect and a civil war following the end of Soviet rule.

As a result, clean water supplies are severely limited and around five million people in Tajikistan and neighbouring regions are threatened by the possible collapse of a vast natural dam at Lake Sarez formed in the early 20th century by an earthquake, Rakhmonov said.

Meanwhile, the southern half of the Aral Sea continues to shrink despite considerable investments to restore wetlands by the World Bank and others.

But for some participants it remained doubtful whether the usually fractious Central Asian leaders are prepared to pay more than lip-service to the need to consult affected residents or cooperate between the countries by sharing information and coordinating the release of water from dams.

A number of the countries did not send ministers to the event and Rakhmonov was the only head of state present.

"The Central Asian nations still approach the issue purely as an engineering problem," the Kyrgyzstan office of the International Crisis Group wrote recently. "Each country has started to view the problem as a zero-sum game."

There are also worries that new demand for Central Asian water could come from neighbouring war-torn Afghanistan as it attempts to develop its northern agricultural sector.

Other delegates were keen to boost cooperation in river basins shared by countries elsewhere such as the water-scarce Middle East, where the overthrow of Iraq's Saddam Hussein has renewed debate over the Euphrates River.

Already severely short of fresh water, the members of the UN's western Asia region such as Egypt, Palestine, Saudi Arabia and Iraq can expect their renewable fresh water reserves to drop by half by 2025, Mervat Tallawy, executive secretary of the UN's economic and social commission for western Asia, said.

The UN's new World Water Development Report estimates that some 2.2 million people around the world died due to water-related diseases last year.

Partly due to global warming, well over two billion people will be suffering from water scarcity by the middle of this century, the report warns.

SPACE.WIRE