Biodiversity in Lake Malawi

Lake Malawi, a deep lake in south-east Africa, is a critical resource not only to the people of Tanzania, Mozambique and Malawi--who rely on it for food, drinking water, irrigation and hydroelectricity--but also as one of the most biologically diverse ecosystems on the planet. It contains more species of fish than any other lake in the world, with 300 already identified and double that number estimated--more than in all of North America. The fact that most of these species are found nowhere else makes the lake a unique and irreplaceable scientific resource.

As the region around the lake becomes more developed, concerns over the impact of intensified agricultural and deforestation practices on critical fish habitats are growing. To assess the problem--and to encourage action before it is too late--scientists with Environment Canada's National Water Research Institute are working with colleagues from Fisheries and Oceans Canada, the United States and Africa to assess the lake's water quality and determine the threats to its sustainability. With funding from the Canadian International Development Agency and the World Bank, the research team is using its expertise in ecology, limnology, chemistry and other disciplines to evaluate the lake and provide recommendations for its sustainable management.

The scientists have discovered that the subsistence agricultural practices of the increasing populations have accelerated soil erosion, water runoff and sediment transport, and caused a deterioration in the water quality of many rivers that feed into Lake Malawi. Eutrophication and excessive sedimentation caused by this phenomenon pose a serious threat to endemic fish species. The burning of biomass to clear lands and renew soil fertility has also increased the atmospheric deposition of nutrients to the lake--a condition that may favour the proliferation of blue-green algae, which are potentially toxic to humans, domestic animals and aquatic life. There is also evidence that concentrations of persistent organochlorines in the lake's fauna may be rising due to atmospheric deposition and the increasing land use of the drainage basin.

Lake Malawi and its many tributaries. The lake is located in the Great Western Rift Valley in south-east Africa.

To maintain the biodiversity of Lake Malawi and support the economic needs of the people who live in the region, the scientists recommend that reduced population growth, sustainable economic development, productive agricultural practices and appropriate fisheries management be implemented as soon as possible. Although the Lake Malawi Biodiversity Project will be completed at the end of July, the people of Tanzania, Mozambique and Malawi will use these findings to develop a sustainable management plan for the conservation and protection of this unique and vital resource.

Why so many species?

Lake Malawi is one of the oldest freshwater lakes in the world--the descendant of a body of water that has been continuously present in the Malawi rift valley for nearly a million years. Because they have had such a long time to evolve and diversify, virtually all of the hundreds of species in Lake Malawi are from the same "flock"--in that they have a common ancestor that arrived there long ago from an inflowing river. Only lakes Baikal and Tanganyika, which also have species flocks, are older. Although its great age partially explains Lake Malawi's rich biodiversity, the question of why there are so many species in a single lake continues to draw scientists from all over the world to this unique resource.

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