The report, "Pilot Analysis of Global Ecosystems (PAGE): Freshwater Systems," says while many regions of the world have ample freshwater supplies, four out of every 10 people currently live in river basins which are experiencing water scarcity. By 2025, at least 3.5 billion people, or nearly 50% of the world's population, will face water scarcity.
In addition, 29 of the world's river basins -- with a projected population of 10 million each by 2025 -- will experience further scarcity.
Further analysis of existing freshwater studies reveals more than 20% of the world's known 10,000 freshwater fish species have become extinct, threatened, or endangered in recent decades.
In the US, which has the most comprehensive data on freshwater species, 37% of freshwater fish species, 67% of mussels, 51% of crayfish and 40% of amphibians are threatened or have become extinct.
"The findings are very disturbing," said Jonathan Lash, WRI president, during a press conference at the annual meeting of the Society of Environmental Journalists. "We essentially gave the world's freshwater systems a physical exam and found out that it is more imperiled than the other ecosystems we studied."
According to the report, much of the degradation of the world's freshwater systems is due to habitat destruction, construction of dams and canals, introduction of non-native species, pollution, and over-exploitation.
The PAGE report estimates dams, diversions or canals fragment almost 60% of the world's largest 227 rivers. The only remaining large free-flowing rivers in the world are in the tundra regions of North America and Russia, and in parts of Africa and South America. About 40,000 large dams over 15 meters high fragment the world's rivers.
Studies of introduction of non-native fish in Europe, North America, Australia, and New Zealand, reveal 77% of them resulted in drastic reduction or elimination of native fish species. In North America, alone, 27 species and 13 subspecies of native fish became extinct in the last century largely due to introduction of non-native fish.
The report said water-borne diseases from fecal pollution of surface waters continue to be a major cause of illness in the Third World. While surface water quality has improved in the US and Western Europe, nutrient loading from agricultural runoff continues to be a major problem.
Although rivers, lakes and wetlands contain only 0.01% of the world's freshwater, and occupy less than 1% of the Earth's surface, global value of freshwater services is estimated in the trillions of dollars. "We need to value freshwater ecosystems not only from the goods they produce, like fish and clams, but also the services they give, like the filters and nurseries that wetlands provide," said Carmen Revenga, one of the report's co-authors.
She added in some countries, growing concern for species extinction, maintenance of pristine habitats and need to maintain the other goods and services ecosystems provide, are driving governments to restore and rehabilitate freshwater systems.
The PAGE report on freshwater systems(http://www.wri.org/wri/wr2000) is the first of five technical reports that will be released in the next six months. Other reports will cover agroecosystems, coastal areas, forests, and grasslands. Taken together, these reports are the first such comprehensive assessment of the state of the world's ecosystems.
They set the stage for the Millennium Ecosystems Assessment (MEA) that will be launched next year by WRI, the United Nations Environment Program, and other international agencies. The MEA is expected to fill in data gaps identified by PAGE reports through participation of hundreds of the world's leading scientists who will be mobilized for this $20 million, four-year effort.
"The challenge for the 21st century is to understand the vulnerabilities and resilience of ecosystems so that we can find ways to reconcile the demands of human development and the tolerances of nature," said Lash.
The World Resources Institute (WRI) is a Washington, DC-based center for research that provides objective information and practical proposals for change to foster environmentally sound and sustainable development. WRI works with institutions in more than 50 countries to bring the insights of scientific research, economic analyses and practical experience to political, business and nongovernmental organizations around the world.
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