Lakes in danger

Posted: 26 March 2008

More than half of the world's five million 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 4 billion people - half of the projected global population - will live in water stressed watersheds, while 1.8 billion of them will be living in regions suffering from absolute scarcity. As more water is withdrawn for human use and more of it is returned to lakes and rivers badly polluted there is less available to maintain vital freshwater ecosystems.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 Tonle Sap River, Cambodia. Credit: Oxfam Australia

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 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.
  • Straddling the borders of Chad, Niger and Cameroon in West Africa, Lake Chad has been a source of freshwater for irrigation projects in all these countries. Over the past 30 years, the lake has seen a dramatic decrease in its size. Since 1963, the lake has shrunk to nearly a twentieth of its original size, due both to climatic changes and to high demands for agricultural water.
  • The Aral Sea, one of the largest inland lakes, has lost four-fifths of its volume since the late 1960s and has receded by up to 250 kilometres, a result of the massive diversion of its two feeder rivers for irrigation of cotton and rice.
  • Madoi County in northwest China’s Qinghai province once had over 4,000 lakes. Over the past two decades, more than half have disappeared as a result of over-use for irrigation and drainage for expanded croplands.
  • Mexico’s largest lake, Chapala, is the primary source of water for Guadalajara’s growing population of over five million. Since the 1970s, it has lost more than 80% of its volume and contracted in size from 1,048 square kilometres to 812 square kms.
  • Mono Lake, North America’s oldest, dating back 760,000 years, has lost 40% of its volume and dropped 11 metres as a result of diversions to provide drinking water to Los Angeles. The lake is now so saline, that it can no longer support most of its native fish species.
  • An estimated 120,000 square kilometres of lakes in Norway are so acidified that fish populations have crashed.

    Lake ChadClick here for maps tracing the shrinkage of Lake Chad and changes in vegetation from 1967 to 2001.

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.

Related link:

Earth Policy Institute 2005 update on lakes

Source:Janet Larsen, "Lakes - An Endangered Species?" Earth Policy Institute, April 2005.