Riverine ecosystems are endangered virtually everywhere by non-sustainable development and the over-use and misuse of limited freshwater resources. More than half of the world's major rivers are either heavily polluted and/or drying up in their lower reaches because of over-use, according to the World Commission on Water for the 21st Century. Of the world's 500 major rivers, 250 are seriously polluted and depleted from overuse. Contamination and overuse of river basins displaced some 25 million environmental refugees in 1998/99.
 
Every day, 2 million tons of human waste are disposed of in water courses.

 40% of water bodies assessed in 1998 in the United States were not deemed fit for recreational use due to nutrient, metal and agricultural pollution.
 
 5 out of 55 rivers in Europe are considered pristine, and only the upper sections of the 14 largest rivers retain 'good ecological status'.
 
 In Asia, all rivers running through cities are badly polluted.

However, two of the world's largest river systems - the Amazon that drains a vast area of South America and the Congo River in sub-Saharan Africa - remain relatively healthy. The main reason: both have few industrial or population centres in their watersheds.

Among the world's most troubled rivers include:

 The Nile River in Egypt. Only 10 per cent of the Nile's waters ever reach the Mediterranean Sea. And this small amount is heavily polluted with agricultural, industrial and municipal wastes. The result: Delta fisheries have been decimated. Of 47 varieties of commercial fish caught in the Delta 30 years ago, only 17 remain. The rest have become extinct or are on the verge of disappearing.
 
 China's Yellow River. Over the past decade, the Yellow River has not reached the Bo Hai Sea on average for three to four months every year. In 1997, the river ran dry in its lower reaches for two-thirds of the year, a record-breaking 226 days. Throughout the 1990s its waters, once a torrent to be revered and feared, have trickled out as far as 600 kms inland.
 
 The Amu Darya and Syr Darya Rivers in Central Asia. The flow of these two major rivers that once fed the Aral Sea which borders Kazakhstan and Uzbekistan in Central Asia have been reduced by three-quarters since the late 1960s. As a consequence, the sea has receded by up to 100 kms. Two-thirds of its volume has been lost.
 
 The Colorado River, USA. Since so much of the river's life giving waters have been siphoned off for irrigation agriculture, little is left by the time the river reaches the Gulf of California in Mexico. Its once rich delta is now a desiccated wasteland where no riverine life survives.

Wetlands

Half the world's wetlands have been lost, with most of the destruction taking place over the past 50 years. Since these fecund areas harbour a wealth of wildlife, their loss has contributed directly to the erosion of biodiversity and species loss.

Take the example of the United States. The lower 48 states have lost over half of their wetlands to development since independence was declared 200 years ago. Wetlands have been whittled away at a relentless pace - decreasing from 200 million hectares in 1780 to 100 million hectares in 2000 - a loss of 247 million acres. A total of 22 states have lost more than 50 per cent of their wetlands, while seven states - Indiana, Illinois, Iowa, Missouri, Ohio and California - lost over 90 per cent.

In some areas of Europe, such as France and Germany, 80 per cent of wetlands have been lost, mostly during the last century.

Wetlands are drained for agriculture, urban expansion and industrial development. They are also drained for urban expansion and industrial development, polluted by runoff from farms, factories and municipal wastes, paved over for roads, mined for peat and minerals, over-run by introduced, non-native species, and grazed to death by domestic animals.

In an effort to preserve the world's remaining wetlands of international significance, a global Convention on Wetlands was signed in Ramsar, Iran in 1971. It is the only environmental treaty for a particular ecosystem and was the first to link conservation with the sustainable use of natural resources.

As an inter-governmental treaty, it provides a common framework for national action and international cooperation for the preservation and management of wetland ecosystems. As of November 2002, there were 133 signatories to the Ramsar Convention with 1,224 wetland sites protected. These total eight per cent of the world's wetlands, or about 105.8 million hectares - an area larger than Portugal.

Originally intended primarily to protect waterbird habitat, the Convention's remit has broadened over the years to recognise wetlands, including coastal wetlands such as mangroves, coral reefs and seagrass beds, both for their biodiversity and the well-being of human communities.

The problem is many of these sites are themselves under threat from development pressures. Listing the site in the Ramsar Convention is no guarantee of protection. Many countries fail to fulfill their pledges and in many cases named sites are being damaged.

National governments need to back up their commitments with appropriate legislation and management systems.

Lakes

Close to half of the world's lakes are degraded from human activities. The main threats include over-fishing, pollution, introduced species and habitat degradation from population growth, expansion of cities and impacts from industrial and agricultural activities.

Lakes on every continent are affected. A recent review of 344 Ramsar sites - which include both wetlands and lake ecosystems - found that an alarming 84 per cent of them were suffering from ecological changes brought on by drainage for agriculture and urban development, pollution, introduced species and siltation.

Furthermore, by 2025 some 3.5 billion people - 48 per cent of the projected global population - will live in water stressed watersheds. As more water is withdrawn for human use and more of it is returned to lakes and rivers badly polluted there is less available to maintain vital freshwater ecosystems. In China, for instance, some 100 lakes are so badly polluted that 70 per cent of their water volume consists of untreated municipal and industrial wastes.

The following examples illustrate the problem:

 Cambodia's Great Lake, Tonle Sap, is suffering from excessive siltation brought on by massive deforestation in its watershed. Human-made structures, including impoundments and dams, have impaired fish pond cultures, disrupted natural flooding cycles and devastated rice crops.
 
 Lake Managua, Nicaragua is now biologically dead due to the massive amounts of untreated sewage and municipal wastes pumped into the lake since 1925.
 
 Lake Ichkeul in northern Tunisia is under threat from plans to divert the rivers feeding the lake to provide water for Tunis and other areas.
 
 Lake Manzala, in Egypt is now devoid of fish because of industrial poisons pumped into it in the 1970s as a result of the expansion of Port Said.
 
 Lake Victoria's water below 30 metres are devoid of oxygen because of the 2 million litres of raw sewage dumped into the lake every year from Tanzania. Introduced species, such as Nile perch and tilapia, have replaced most of the native fish species of cichlids in the lake: they were reduced from 85 per cent of biomass to less than 5 per cent today.
 
 Polluting factories spew some 74 million cubic meters of wastes into Siberia's Lake Baikal. By the mid-1990s some 20 square kilometers of the lake's bottom registered very low oxygen levels due to pollution.

The state of the world's freshwater lakes mirror the problems afflicting the world's watersheds and rivers. Without integrated management plans freshwater resources will continue to deteriorate.

Sources: People and the Planet, World Water Assessment Programme