The world's rivers are in a crisis of ominous proportions, according to a new global analysis.

The report is the first to simultaneously account for the effects on the health of the world's rivers of such things as pollution, dam building, agricultural runoff, the conversion of wetlands and the introduction of exotic species.

The resulting portrait is grim, revealing that nearly 80% of humans live in areas where river waters are highly threatened, posing major problems to both human water security and aquatic environments where thousands of species of plants and animals are at risk of extinction.

The report was authored by an international team led by Charles J. Vörösmarty of the City University of New York, an expert on global water resources, and Peter B. McIntyre, a professor of zoology at the University of Wisconsin-Madison's Center for Limnology and an expert on freshwater biodiversity.

Says Vörösmarty: "What we've discovered is that when you map out these many sources of threat, you see a fully global syndrome of river degradation. We find a real stew of chemicals flowing through our waterways. We know it is far more cost effective to protect these water systems in the first place. So, the current emphasis on treating the symptoms rather than the underlying causes makes little sense from a water security standpoint or a biodiversity standpoint, or for that matter an economic standpoint."

Among the startling conclusions: rivers in the developed world, including much of the United States and Western Europe, are under severe threat despite decades of attention to pollution control and investments in environmental protection. Huge investments in water technology and treatment reduce threats to humans, but mainly in developed nations, and leave biodiversity in both developed and developing countries under high levels of threat, according to the new report.

"What made our jaws drop is that some of the highest threat levels in the world are in the United States and Europe," says McIntyre, who began work on 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."

Rivers of the world least at risk are those where human populations are smallest. Rivers in arctic regions and relatively inaccessible areas of the tropics appear to be in the best health.

The hard lessons learned by the developed world, says McIntyre, can help governments and planners in other parts of the world avoid the same mistakes and experiment with strategies for promoting water security and protecting biodiversity. Instead of investing billions of dollars in expensive remediation technologies, strategies such as protecting watersheds, for example, can reduce the costs of drinking water treatment, preserve floodplains for flood protection and enhance rural livelihoods.

The analysis used data sets on river stressors around the world. Built into state-of-the-art computer models, the data yield maps that integrate all of the individual stressors into aggregate indices of threat. The same strategy and data, say Vörösmarty and McIntyre, can be used by governments worldwide to assess river health and improve approaches to protecting human and biodiversity interests.

"We've created a systematic framework to look at the human water security and biodiversity domains on an equal footing," Vörösmarty says. "We can now begin presenting different options to decision makers to create environmental blueprints for the future."

The work underpinning the study was funded by the Earth System Science Partnership, an international scientific consortium that supports research on global environmental change; the Bonn-based Global Water System Project, an interdisciplinary research effort to articulate human-water interactions; and Paris-based DIVERSITAS, an international collaborative whose mission includes providing accurate scientific information related to issues of biodiversity. The work was also supported by the National Science Foundation, NASA, the Global Environmental Facility, and the Society for Conservation Biology's Smith Fellowship Program.