A global analysis concludes that rivers, which are the primary source of water and livelihood for billions of people around the world, are in a crisis state as a result of human activities, such as dam building, agricultural run-off and chemical pollution.
According to the study, nearly 80 percent of the world's population lives in areas where rivers and water systems are severely threatened by pollution, rapidly growing human populations and the accidental redistribution of plants and animals that destroy indigenous marine life.
Rivers are the single largest renewable source of fresh water for humans, who use them for drinking water, fishing, bathing and recreational activities.
But study co-author Peter McIntyre, a zoologist and river specialist at the University of Wisconsin, says the world's rivers are having trouble recovering from the fallout of global economic development.
The report found, surprisingly, that water systems in the United States, Western Europe and other industrialized nations were at the greatest risk, despite decades of pollution-control efforts and the technological means to protect and restore river ecosystems.
The report warns that similar degradation is occurring in the developing countries, which don't have the resources to invest in technologies to clean up their rivers, and where population has been growing very rapidly.
The study found the healthiest rivers are those in areas where human populations are the smallest.
"Many billions of people live in areas where the fundamental quantity and quality of water that they have access to are highly threatened. That suggests that there are real problems in the present and we expect they are only get worse as human populations grow, as resource use per capita continues to increase into the future. And then you overlay climate change on that and things could get very scarey," McIntyre said.
As the quality of the world's rivers declines, McIntyre says a major concern is the health of fisheries, the source of food and livelihood for hundreds for millions of people.
"Many of the world's largest fresh water fisheries are in the great rivers of the world, the Mekong, the Amazon, lots of rivers in tropical Africa. So, there are enormous fisheries that employ and feed large segments of the population in the developing world. And those really are at risk from introduced species, from over-fishing, from pollutants in the fish. You put that all together and there's real cause for concern," he said.
McIntyre says developing countries, with the aid of richer nations, should take a lesson from the developed world's experiences. They should avoid making costly investments in water clean-up technology in favor of strategies to conserve the health of their river environments.
Such strategies include protecting water sheds from polluters to keep the cost of drinking water down and preserving flood planes for flood protection.
The assessment by McIntyre and colleagues on the health of the world's rivers is published this week in the journal Nature.