By Adam Vaughan
The world's rivers are so badly affected by human activity that the water security of almost 5 billion people, and the survival of thousands of aquatic species, are threatened, scientists warned.
The study, conducted by institutions across the globe, is the first to simultaneously look at all types of human intervention on freshwater - from dams and reservoirs to irrigation and pollution. It paints a devastating picture of a world whose rivers are in serious decline.
While developing countries are suffering from threats to both water security and biodiversity, particularly in Africa and central Asia, the authors were surprised by the level of threat posed to wildlife in rich countries.
"What made our jaws drop is that some of the highest threat levels in the world are in the United States and Europe," said Prof Peter McIntyre, one of the lead authors, who began the project as a Smith Fellow at the University of Michigan.
"Americans tend to think water pollution problems are pretty well under control, but we still face enormous challenges."
Some of the worst threats to aquatic species in the US are in the south-eastern states. Prof Charles Vörösmarty of the City University of New York, lead author and an expert on global water, said the impact on wildlife in developed countries was the result of river systems that had been heavily engineered and altered by man. "With all the protection the EU has in place, it was surprising to see it was a hotspot for biodiversity loss. But for a long time Europeans have altered their landscapes, including the removal of 90% of wetlands and floodplains, which are crucial parts of river ecosystems," he said.
The team behind the report, published in the journal Nature, examined datasets to produce a map of how 23 different human influences - such as dams, the introduction of alien non-native fish, and pollution - affect water security and biodiversity. Previous studies have tended to look at just one influence at a time.
Even the world's great rivers, such as the Yangtze, the Nile and the Ganges, are suffering serious biodiversity and water security stress.
Despite their size, more than 30 of the 47 largest rivers showed at least moderate threats to water security, due to a range of human impacts such as pollution and irrigation. Even the Amazon, considered to be relatively pristine, still has human fingerprints on it, said Vörösmarty.
"While the Amazon is in generally good shape, in the upstream regions, such as Peru, there are many high density areas of people that inject threat into the system.
"The legacy of that human threat passes downstream into the remote forested areas of the river."
Globally between 10,000 and 20,000 aquatic wildlife species are at risk or face extinction because of the human degradation of global rivers, the report said. The world's least affected rivers, the authors found, were those furthest from populated areas, such as remote parts of the tropics, Siberia and elsewhere in the polar regions.
Vörösmarty said he hoped the global report would highlight the need to address the root causes of the degradation of rivers. "We're spending trillions of US dollars to fix a problem we've created in the first place. It's much cheaper to treat the causes rather than the symptoms, which is what we do in the developed world today," he said.
In Britain rivers have been getting cleaner over the past decade. But a report by the UK's Environment Agency last year admitted only five of 6,114 rivers in England and Wales were considered pristine and three-quarters were likely to fail new European quality standards for various reasons.
