Along the shore of Lake Victoria
Among the great variety of inland water bodies, perennial lakes comprise 1.7 million km2, one million km2 of which are large lakes (larger than 100 km2). Swamps, marshes and other wetlands account for about 4 million km2. The distribution and size of lakes vary considerably among continents. North America possesses the greatest freshwater large lake surface area, whereas large lakes are uncommon in South America. Although there is a large number of lakes in the temperate zone of Europe and Asia, lakes are less common in tropical Asia -- however some, such as the Great Lake on the Tonle Sap in Cambodia and Lake Tempe in Sulawesi (Indonesia) are of the utmost importance to fisheries.
Africa, especially East Africa, is endowed with numerous lakes that support very important fisheries, in turn providing a livelihood to millions of people and contributing significantly to food supply. In many of these lakes fisheries are reaching a state of maturity and consequently management problems are rising. For 11 lakes, shared by 11 countries of eastern Africa, fisheries employs close to half a million people, with perhaps three times as many engaged in secondary activities and related services, thus supporting about 4 percent of the population of the region as a whole.
Fish resources in lakes
The degree of resource utilization differs greatly from lake to lake and according to two main types of fisheries: demersal/inshore and pelagic/offshore. Currently, the demersal/inshore resources are heavily exploited or overexploited. African large lakes are receiving adequate biological attention through a number of international activities, with research focusing particularly on lakes Victoria, Tanganyika and Malawi. However, governmental support in some African countries is still low, with little money allocated from national budgets for their development. In Asia, there is a relatively advanced national capacity for the development of enhanced fisheries but less experience in social and political issues.
Large lakes of the world
Courtesy of The Great Globe Gallery
Impacts on lakes
Negative impacts on lake ecosystems result from environmental disruptions in lake basins: rapid siltation caused by accelerated soil erosion in catchment areas; irreversible uptake of water and/or salinization due to irrigation; eutrophication; contamination with toxic chemicals and mine tailings; acidification. Large lakes such as the Caspian Sea, Aral Sea, lakes in northern America and some lakes in Africa have been affected by human impacts in their catchments and point-source pollution. Effective integrated watershed management will involve not only soil conservation measures, but will also require changes in the way water moves through the agro-ecosystem. Opportunities exist here for case studies and for new management strategies.