Two or more countries may have jurisdiction over portions of a geographical area which constitutes a hydrogeological unit as the catchment area for a single river. In the absence of a coordinated approach to the development of the river basin, one or more of these countries may be placed at a disadvantage. Water control projects (flood protection, dams, soil conservation) in one country may adversely effect the territory of another through which the same river passes. Disposal of sewage or industrial waste into a river by an upstream country and diversion of water from rivers flowing into a country may adversely affect its domestic water supply, irrigation requirements, power generation, etc. The withdrawal of underground water in one country may reduce the available river water in a second country.
Of 200 international river basins in a recent review, 148 (70%) are shared by 2 countries, 30 by 3 countries and 22 by from 4 to 10 countries. About 25% of the countries of the world are situated entirely within international river basins and, except for island countries, almost all countries are involved in the problems of international river basins to a greater or lesser extent. The number of related bilateral and multilateral treaties is about 300. Yet over one third of the 200 major international river basins are not covered by any international agreement, and fewer than 30 have any cooperative institutional arrangements. River water disputes have already occurred in North America (the Rio Grande), South America (the Rio del la Plata and Parana), South and Southeast Asia (the Mekong and Ganges), Africa (the Nile), and the Middle East (the Jordan, Litani, Orontes, and the Euphrates). Pollution, impoundment and diversion of water by upstream nations is likely to be a growing source of international tension and insecurity.
Africa is facing a continent-wide shortage of potable water. Overall water quality has declined markedly during the past decade due to progressive land clearance, expanding human population, and rapid urbanization, all of which are socially and economically driven changes. Both biological diversity and water management objectives are threatened through the introduction of exotic plants and fish into reservoirs and lakes throughout the continent, with the most poignant example being Lake Victoria. Fish catches have declined drastically throughout Africa due to over-exploitation, declining water quality, and introduction of exotic predators, thus restricting one of the most important protein sources for the rapidly expanding human population. Most problems with African freshwater ecosystems are associated with a failure to develop sustainable management plans that recognize the necessity for multipurpose use of resources. In addition, a majority of freshwater ecosystems of the continent are shared by several nations, and the lack of enforceable transboundary protocols hinders sound management. The political and policy issues surrounding multinational management of the Lake Victoria basin, for example, illustrates one of the dilemmas facing ecologists and water managers.