Death of the world's rivers

Disaster warning from UN as investigation reveals half of the planet's 500 biggest rivers are seriously depleted or polluted

The world's great rivers are drying up at an alarming rate, with devastating consequences for humanity, animals and the future of the planet.

The Independent on Sunday can today reveal that more than half the world's 500 mightiest rivers have been seriously depleted. Some have been reduced to a trickle in what the United Nations will this week warn is a "disaster in the making".

From the Nile to China's Yellow River, some of the world's great water systems are now under such pressure that they often fail to deposit their water in the ocean or are interrupted in the course to the sea, with grave consequences for the planet.

Adding to the disaster, all of the 20 longer rivers are being disrupted by big dams. One-fifth of all freshwater fish species either face extinction or are already extinct.

The Nile and Pakistan's Indus are greatly reduced by the time they reach the sea. Some, such as the Colorado and China's Yellow River, now rarely reach the ocean at all. Others, such as the Jordan and the Rio Grande on the US-Mexico border, are dry for much of their length.

Even in Britain, a quarter of the country's 160 chalk rivers and steams - such as the Kennet in Wiltshire, the Darent in Kent, and the Wylye in Wiltshire - are running out of water because too much is being abstracted for homes, industry and agriculture.

This week an influential UN report will officially warn the world's governments of an "alarming deterioration" in the planet's rivers, lakes and other freshwater systems. Klaus Toepfer, the executive director of the United Nations Environment Programme, told the IoS yesterday that the state of the world's rivers is "a disaster in the making".

The UN's triennial World Water Development Report, compiled for an international conference in Mexico City which opens on Thursday, warns that "we have hugely changed the natural order of rivers worldwide", mainly through giant dams and global warming. Some 45,000 big dams now block the world's rivers, trapping 15 per cent of all the water that used to flow from the land to the sea. Reservoirs now cover almost 1 per cent of land surface.

The UN report says that demand for them "will continue to increase", but recommends that they should be barred from the world's remaining, undammed "free-flowing" rivers.

The United States has dismantled 465 dams in recent years, mainly for environmental reasons. But last week, in an abrupt U-turn, it signalled that it was about to embark on its biggest dam-building campaign in decades, when the Washington State legislature passed a bill to allow the federal government to build a series of dams on the Columbia, the West's largest river.

Global warming is endangering even the rivers that have largely escaped damming.

The relatively untamed Amazon was hit by its most serious drought on record last autumn. And salmon are dying in Alaska's Yukon River - the world's longest undammed watercourse - because its waters are getting too hot.

On Tuesday an international day of action will see demonstrations across the globe to draw attention to rivers' plight.