(IPS) feature

More than half the world's lakes and reservoirs suffer from overuse and pollution, water experts warned recently.

Holding nearly 90 percent of all surface liquid fresh water, the world's five million lakes and reservoirs are being overdrawn by irrigation projects and contaminated by toxic chemicals and nutrients from industry, farms, and sewage, they said.

Even though the amount of fresh water currently stored in lakes worldwide is about 35 times the amount found in rivers, governments and conservationists generally have ignored lakes, according to Hideaki Oda, secretary general of the Third World Water Forum, scheduled for 2003 in Japan.

''Until now, policy makers have focused on rivers, tidal basins and oceans, excluding a discussion of lakes,'' Oda said in a statement released at the opening day of week-long talks on the subject in Shiga, Japan.

Scientists and conservationists urged action on lake conservation because, in addition to being important sources of water, they are critical to agriculture, commerce, tourism, transportation, and energy production.

''Natural lakes, especially large ones, are of great economic, ecological, and cultural importance, with at least one billion people depending on them for their livelihood and for drinking water,'' said Masahisa Nakamura, director of Japan's Lake Biwa Research Institute.

Increased irrigation

Some lakes are so overdrawn they are disappearing, the scientists said. In China, 543 large and medium-sized lakes disappeared between 1850 and 1980 when water was diverted for irrigation. The Aral Sea, located between Kazakhstan and Uzbekistan, has shrunk from the world's fourth largest lake to eighth largest because of increased irrigation in the region.

''If a lake dies, it affects people for hundreds of miles around it,'' said Sven Erik Jorgensen, head of the International Lake Environment Committee (ILEC), a Japan-based organisation that works with the United Nations Environment Programme.

Developing nations, he said, are especially at risk because without abundant fresh water, they will struggle to develop economically.

''People in the developing world are much more dependent on lakes than residents of industrialised countries,'' he said.

Some of the most threatened lakes in developing countries, according to conference participants, include Africa's Lake Victoria and Lake Chad, China's Taihu Lake, Thailand's Songla Lake, and India's Lake Bhopal.

Withdrawals of water from lakes, their tributaries, or the groundwater feeding them have increased dramatically over the past century, researchers said. Since 1900, such water withdrawals worldwide have increased to 3,800 cu km per year, from 578 cu km per year.

The UN's recent Global Environment Outlook report estimated that global fresh water consumption rose six-fold between 1900 and 1995 - at more than twice the rate of population growth.

Most of the world's lakes suffer from eutrophication, a process in which an over-abundance of nutrients from agriculture or industry causes a rapid growth of aquatic plants that choke off other organisms. The ILEC said 54 percent of the lakes in Asia suffer from this, compared with 53 percent in Europe, 28 percent in North America, and 41 percent in South America.

Acid rain problem

Acid rain, caused by sulphur and nitrogen oxides emitted by coal-powered industries, is another serious problem impacting lakes worldwide, researchers said. This is so especially in Australia, Canada, China, Europe, Japan, New Zealand, and the United States.

''Many lakes in Scandinavia and the affected regions of North America have become so acidic in the past few decades that they can no longer sustain the diverse forms of life originally found there,'' the researchers who met in Shiga said in a statement.

Once a lake becomes degraded, it takes a lot of effort and resources to restore it. ''As a consequence, successful restorations are rare, particularly in the case of large lakes,'' the statement added.

A few lakes, including Lake Washington in the United States, have been restored through improvements in wastewater treatment facilities that have been designed to remove excess nutrients, Nakamura said.

Many of the larger lakes in Europe, including Lake Constance and Lake Geneva, also have benefited from advanced wastewater treatment, which has significantly improved water quality since the early 1980s despite ecological stress from urban and agricultural activities.

''Unfortunately, it is also a remedy that is usually beyond the means of developing countries,'' Nakamura said.

Some developing nations, however, have succeeded in improving small and shallow lakes, particularly in urban areas, by installing sewage treatment plants, Nakamura noted. The Xiamen city government in China, for example, has constructed several sewage treatment facilities to clean up polluted lakes within the metropolitan area.

These cases, says Nakamura, provide ''some confidence in lake restoration in developing countries''.