EAST AFRICAN LAKES

Mountains and lakes of East Africa. group of lakes in East Africa. The majority of the East African lakes lie within the East African Rift System, which forms a part of a series of gigantic fissures in the Earth's crust extending northward from the Zambezi River valley through eastern and northeastern Africa and the Red Sea to the Jordan River valley in southwestern Asia. In East Africa itself the southern, eastern, and western branches of the system can be discerned. Occupying the Southern Rift Valley is Lake Nyasa (Lake Malawi), which drains into the Zambezi River. Marking the course of the Western Rift Valley are Lakes Tanganyika, Kivu, Edward, and Albertthe first two of which are situated within the drainage basin of the Congo River, while the other two constitute part of the Nile River drainage system. With the exception of Lake Rudolf (Lake Turkana), the lakes found in the Eastern (Great) Rift Valley are smaller than those of the Western Rift and constitute several independent inland drainage basins. Located in a shallow downwarping between the Eastern and Western Rift highlands is Lake Victoria, which among the freshwater lakes of the world has a surface area that is second only to that of Lake Superior in North America. On a smaller scale, East Africa also includes some fine examples of crater lakes, and on Mount Kenya and in the Ruwenzori (Rwenzori) Range are found glacial tarns, small lakes each of which occupies a basin, or cirque, scraped out by a mountain glacier. Of the eight largest lakesVictoria, 26,828 square miles (69,485 square kilometres) in area; Tanganyika, 12,700; Nyasa, 11,430; Rudolf, 2,473; Albert, 2,160; Kivu, 1,040; Rukwa, 1,000; and Edward, 830only one, Rukwa, in Tanzania, lies wholly within a single political entity. The northern shore of Kenya's Lake Rudolf is in Ethiopia; Lake Victoria is divided among Uganda, Tanzania, and Kenya. In the west the international boundary between Uganda and Congo (Kinshasa) runs through the centre of Lake Albert; the same boundary places two-thirds of Lake Edward in Congo and the remainder in Uganda. Lake Kivu lies between Rwanda and Congo; the waters of Lake Tanganyika are shared among Tanzania, Congo, Burundi, and Zambia. Malawi and Mozambique have territorial waters on Lake Nyasa, and, since its independence, Tanzania has also advanced claims to its territorial waters because it also occupies a part of the lakeshore. group of lakes lying within the great East African Rift System that runs from the Red Sea in the north to the Zambezi River in the south. The group includes lakes lying in Ethiopia, Kenya, Uganda, Congo (Kinshasa), Rwanda, Burundi, Tanzania, Zambia, Malawi, Mozambique, and Zimbabwe. The eight largest lakes are Victoria, Tanganyika, Nyasa (Malawi), Rudolf (Turkana), Albert, Kivu, Rukwa, and Edward. These range downward in size from Lake Victoria, covering 26,828 square miles (69,485 square km) to Lake Edward, 830 square miles (2,150 square km); surface elevations increase from Lake Rudolf at 1,230 feet (375 m) to Lake Naivasha at 6,180 feet (1,884 m) above sea level. The lakes must have been formed after the landscapes in which they are set. In some lakes volcanic activity has played a part in blocking drainage and shaping shorelines. Raised beaches indicate that the lake levels were higher and their surfaces more extensive during rainy phases of the Pleistocene Epoch (1,600,000 to 10,000 years ago). The fossil record suggests that the organic content of Lakes Edward and George was sharply reduced during a period of intense volcanic activity. The lakes lying in inland troughs at 2,000 feet (610 m) or less above sea level, have a hot, dry climate. At higher elevations, climatic conditions approach those of the flanking uplands. Sudden and dangerous storms can arise over the waters of the major lakes. Rainfall is closely correlated to variations in lake levels. Other factors affect longer-term level fluctuations, among them the intermittent blockage of outlets by silt consolidated by swampy growth. Most of the lakes have a rich and varied fish life, although fish transplantation by humans has greatly modified some habitats. On land, vegetation varies from semidesert to patches of closed evergreen forest, with bushland and thicket, grassland, savanna, or open woodland occuring between the two extremes, depending on location; the creation of national parks and game reserves has increased wildlife populations. The lakes' two major resources are fishing and hydroelectric power. The major lakes are reasonably accessible by road and air, with the exception of Lake Rudolf, which has poor road connections. Additional reading Leslie Brown, East African Mountains and Lakes (1971), is a useful introduction to the region's scenery and wildlife. L.C. Beadle, The Inland Waters of Tropical Africa, 2nd ed. (1981), has a strong East African section and contains an extensive bibliography. David Keith Jones, Faces of Kenya (1977), includes chapters on the lakes. Paul H. Temple, The Lakes of Uganda, in S.H. Ominde (ed.), Studies in East African Geography and Development (1971), pp. 8698, classifies the lakes in physical terms. M.J. Mann, Freshwater Fisheries, in W.T.W. Morgan (ed.), East Africa: Its Peoples and Resources, 2nd ed. (1972), pp. 229242, gives a brief account of the fisheries of the individual lakes of Kenya, Uganda, and Tanzania. Victor C.R. Ford, The Trade of Lake Victoria: A Geographical Study (1955), describes against a historical background the international trade achieved within this area in the preindependence period. Samuel John Kenneth Baker Geology, climate, and hydrology The East African rifts attained their present form mainly as a result of Pleistocene earth movements from 1,600,000 to 10,000 years ago, and the lakes must have been formed after the landscapes in which they are set. The shallowness of such lakes as Albert (maximum recorded depth 190 feet) and Edward (367 feet) is the result of the thick layers of sediment upon which they rest. In some lakes, too, volcanic activity has played a part in blocking drainage and shaping shorelines. Raised beaches indicate that the lake levels were higher and their surfaces were more extensive during rainy phases of the Pleistocene Epoch. In the Eastern Rift, for instance, Lakes Rudolf and Baringo were formerly part of one lake, from which there was a link via the Sobat River with the White Nile. Subsequent drier conditions caused the eastern lakes gradually to dwindle in size, with many fluctuations, to their present independent status. The lakes of the Western Rift have experienced their own geologic changes. Before the geologically recent blocking of the rift by the eruption of the Virunga Mountains, the drainage of Lake Kivu was probably northward into the Nile. The fossil record suggests that the organic content of Lakes Edward and George was considerably reduced during a period of intense volcanic activity around their shores, although several species of fish (e.g., Tilapia nilotica) appear to have survived. Toward the end of the Middle Pleistocene (about 100,000 years ago), when the rise in the shoulders of the Western Rift resulted in the reversal of the westward-flowing drainage of such rivers as the Kagera, Katonga, and Kyoga-Kafu, Lakes Victoria and Kyoga were formed by water diverted from the northern section of the rift. Eventually, however, the drainage of most of Uganda returned to the Western Rift and to the Nile. The subsequent reductions in the level of Lake Victoria are indicated by a series of strandlines around its shores. Those East African lakes that lie in inland troughs at altitudes of about 2,000 feet or less have a hot, dry climatic environment with a high potential evaporation. In the higher parts of the rift floors, however, climatic conditions approach those of the flanking highlands. In the Western Rift moist air from the Congo basin is a source of the more humid conditions prevailing over Lakes Tanganyika and Kivu. The glacial tarns of Mount Kenya and the Ruwenzori Range are in the frigid zone. Large lakes tend to create or influence their own climates, and this effect is most marked on the western and northern margins of the immense mass of Lake Victoria. There, in a zone 30 to 50 miles wide, temperatures rarely rise above 80 F (27 C) or fall below 60 F (16 C), and rainfall is well distributed throughout the year. Moreover, annual rainfall is high, being heaviest over the lake and decreasing inland from an average of 50 to 60 inches (1,300 to 1,500 millimetres) at the lake shores. At the northern end of Lake Nyasa, an annual rainfall total of about 120 inches results from similar influences reinforced by air convergence caused by the funnel-shaped relief at the head of the lake. Sudden and dangerous storms are likely to arise over the waters of all the major lakes. The levels of the East African lakes are perceptibly sensitive to climatic fluctuations. Average seasonal ranges of level are small: no more than a foot on Lake Victoria, 1.3 feet on Lake Albert, and three to four feet on Lake Nyasa. Longer-term fluctuations, with consequential effects on the shorelines, are greater: during the 20th century the extreme range recorded on Lake Victoria has been 10.3 feet, compared with 17.3 feet on Lake Albert and 18.8 feet on Lake Nyasa. In each case the recorded maximum occurred in the early 1960s. The effects of drought are enhanced in small, shallow lakes: Lake Nakuru, in Kenya, dried up completely in 193940; at the end of 1949 Lake Rukwa was estimated to be one-fifth its normal size; and Lake Chilwa, in Malawi, suffered a drastic reduction of area in 196768. There is a significant correlation between rainfall and variations in the level of Lake Victoria, and Lakes Kyoga and Albert followwith an appropriate time lagthe conditions of Lake Victoria. In addition to rainfall, other factors affect the longer-term fluctuations of Lakes Tanganyika and Nyasa. The Lukuga River outlet of Lake Tanganyika tends to become blocked intermittently by silting, consolidated by swampy growth. Similarly, in the flat valley of the upper Shire River, periods of erosion alternate with the building of bars of silt and sand reinforced by reeds. As a result, between 1915 and 1935 there was virtually no outflow from Lake Nyasa. Many of the lakes, especially those in the Eastern Rift, are brackish, but Baringo and Naivasha are exceptions in that they are freshwater lakes and are believed to have subterranean outlets. At the other extreme of salinity, Magadi is a soda lake, in which the continuing source of sodium carbonate (natron) appears to be alkaline waters of deep-seated origin. Lakes Edward and George have the highest salinities among the lakes of the Western Rift, but the alkalinity is not excessive. The problem of the deeper lakes, such as Tanganyika, Nyasa, and Kivu, is that their deeper waters are permanently deoxygenated and thus constitute a biological desert: 75 percent of the volume of Lake Tanganyika and 99 percent of that of Kivu are within this category. Moreover, all three lakes contain lethal amounts of hydrogen sulfide in their deeper waters, and Lake Kivu also contains vast quantities of methane. Plant and animal life The vegetation setting of the lakes varies from the semidesert, in which Lake Rudolf is situated, to the patches of closed evergreen forest on the western and northern shores of Lake Victoria. Between the two extremes and in accordance with the position of the individual lakes, bushland and thicket, grassland, savanna, or open woodland occur. The oil palm, which is characteristic of western Africa and of the Congo region, is found on the shores of Lake Tanganyika. Heavily populated and intensively cultivated areas marginal to Lakes Victoria and Nyasa present vegetation types that have been much modified by human activity. The lakeshores may consist of open landscapes of headland or beach or may contain plants associated with swamps, such as the giant sedge, Cyperus papyrus, which is the most prevalent. Among the main genera of fish in the East African lakes are the mouthbreeders Tilapia, much the most important in number of species and in total quantity; Haplochromis (which, like the Tilapia, belong to the Cichlidae family), a group of small perchlike fish; Clarias (barbel) and Bagrus among the catfish; Hydrocynus (tiger fish); various carps, including Labeo, Barilius, and Barbus; Protopterus, a lungfish; Mormyrus, a member of the elephant-snout fish family; and Stolothrissa tanganicae (dagaa), a small sardinelike fish. The more strongly saline lakes, such as Nakuru, Elmenteita, Manyara, and, above all, Magadi and Natron, have a severely limited fish life. Lake Kivu also has a fish population that is neither varied nor abundant. Although fish are present in enormous quantities in Lake Rukwa, the number of species is not large, and the stock is dominated by the endemic Tilapia rukwaensis. Successive droughts such as that of 1949 explain why there are so few species in Lake Rukwa; the years immediately following 1949, on the other hand, provide an excellent example of the amazing recovery powers of tropical fish populations. The majority of the lakes, though, have a rich and varied fish life, of which a high proportion of species are endemic to the individual lake. The Cichlidae, for example, are especially prone to form new species, and there are between 100 and 200 species of the family in Lakes Victoria and Kyoga. Lake Albert has a fish life that is related to that of the Nile; it includes Nile perch, tiger fish, and Polypterus (bichir). The physical barrier of Murchison Falls, situated near the northern end of Lake Albert, marks the frontier of a separate faunal province formed by Lakes Victoria and Kyoga. Several of the Lake Albert genera are not found in these two lakes, which contain many unique species. Similarly, the rapids on the Semliki River have prevented the introduction of fish species from Lake Albert into Lakes Edward and George, which otherwise are particularly rich in fish. On the other hand, the presence of Nile perch, tiger fish, and bichir in Lake Rudolf serves to indicate its former connection with the Nile. The transplantation of fish by humans, however, has caused a man-made zoogeographic revolution, the full effects of which cannot yet be discerned. The hippopotamus is ubiquitous around the lakeshores, except those of Lake Kivu; the crocodile is also widespread, although absent from Lakes Edward, George, and Kivu, each of which is sheltered from the spread of this reptile by falls in the outflow river, with cool mountain torrents and sunless forest as additional deterrents. Traditionally there has been an inverse relationship between the density of game and that of human settlement. The establishment of national parks and game reserves, however, has encouraged the increase of game population, although widespread poaching has created serious problems. Among the variety of game to be seen in the neighbourhood of the lakes are elephant, buffalo, and various antelopes. Among the resident and migrant birds in evidence, waterfowl are especially noticeable. Several of the Eastern Rift lakessuch as Nakuru, Elmenteita, and Manyaraare famous for their vast congregations of flamingos. Forming the basis of a national park in which the emphasis is on aquatic birds, Lake Nakuru is an ornithologist's paradise; Lake Edward and the Kazinga Channel are also notably rich in birdlife. The fish-eating birdscormorants, darters, and kingfishersare also part of the ecology of the lakes. Study and exploration Following in the track of earlier Arab trading expeditions, the British explorers Sir Richard Burton and John Hanning Speke reached the eastern shore of Lake Tanganyika in 1858. It was there, at Ujiji, that David Livingstone, the Scottish explorer-missionary who had pioneered the Shire River route to Lake Nyasa in 1859, was met by the Welsh explorer Henry Morton Stanley in 1871, after which the two subsequently made a reconnaissance of the northern part of the lake. Then, in 1874, in the course of his eastwest traverse of the continent, the English traveler Verney Lovett Cameron explored the Lukuga River outlet on the western shore of Tanganyika. While Burton remained at Tabora in 1858, Speke journeyed northward and became the first European to view the waters of Lake Victoria. In 1862, after he returned to East Africa with a fellow countryman, James Augustus Grant, Speke stood above the Ripon Falls, which he proclaimed as the source of the Nile. The details of the Lake Victoria shoreline were filled in by Stanley when he circumnavigated the lake in 1875. Meanwhile another Englishman, Samuel White Baker, and his wife, Florence, had approached the East African lakes from the north, reaching Lake Albert in 1864. In 1888 to 1889 Stanley, in company with Mehmed Emin Pasa (or Pasha), the German explorer, traced the Semliki River to its source in Lake Edward. Finally, in 1894, a German explorer, Adolf von Gtzen, became the first European to visit Lake Kivu. During the 1880s Europeans explored the lakes of the Eastern Rift. Lakes Magadi and Naivasha were visited by a German traveler, Gustav Fischer, in 1883, and in the same year the Scottish explorer Joseph Thomson reached the shores of Lake Baringo. Five years later Count Smuel Teleki and Ludwig von Hhnel reached Lake Rudolf. Considerable scientific study of the lakes region has been conducted since that time. The people and the economy Although not all the shores of Lake Victoria are well settled, the lands marginal to the lake are among the most densely populated in Africa. The best-known groups inhabiting these marginal lands are the Ganda, Soga, Luhya, Luo, Sukuma, and Haya, all of whom, except for the Luo (who are Nilo-Saharan speakers), are Bantu-speaking. The eastern margins of Lake Kivu reflect the high population density of Rwanda, and the lowlands at the northern and southern ends of Lake Nyasa are also well populated. In general, though, the shores of the Eastern and Western Rift lakes are sparsely settled. Resource exploitation Fish constitute one of the major resources of the East African lakes, but the degree of exploitation varies considerably from lake to lake. Uganda, for example, possesses one of the largest freshwater fishing industries in the world, while production from Kenya is appreciably lower. The potential of Lake Rudolf, well-stocked with Nile perch, has been only partially realized, whereas to the south the waters of the much smaller Lake Baringo have been more strongly exploited. Black bass and several species of Tilapia, both of which were introduced, form the basis of the commercial fishery of Lake Naivasha; the lake is also a popular weekend resort for Nairobi residents, many of whom are attracted by the sport fishing. At Lake Magadi, on the other hand, soda ash, which is the leading mineral export of Kenya, is extracted and refined. The strongly developed Ugandan fishery of Lake Kyoga is largely based on introduced Nile perch; and although Lake Victoria is considered to be essentially a Tilapia fishery, there are also important catches of other species, including Nile perch. The fisheries of Lake Victoria are important as a source of protein for the rural and urban population living in the vicinity. The Luo and the Sese Islanders have shown a marked interest in the industry, which is practiced by independent fishermen, typically using planked canoes with outboard motors. Another important resource at Lake Victoria is the Owen Falls power station at Jinja, which provides electricity for use in Uganda and Kenya. In addition, the dam at the falls enhances the potential of Lake Victoria as a storage reservoir for the Nile River, in the process raising the average level of the lake by three feet. The Lake Victoria region has great potential for economic growth, although greater cooperation among its bordering states is needed to realize this potential. The varied fish life of Lake Albert includes Nile perch and two genera of tiger fish, of which one, Alestes, provides two-thirds of the total weight landed on the Uganda shores of the lake. It is believed, however, that the total catch is below the maximum sustainable yield of the lake. A tourist attraction adjacent to Lake Albert is the Murchison Falls (Kabalega) National Park, which extends down to the narrowing outlet at the northern end of the lake. Lakes Edward and George support remarkably fertile fisheries. The Congo (Kinshasa) shores of Lake Edward are within the Virunga National Park, while the Ugandan portion of the lake lies within the Queen Elizabeth (Ruwenzori) National Park. Close to the northeastern shore of Lake Edward, Lake Katwe, which lies in one of the numerous shallow craters within the EdwardGeorge branch of the Western Rift, is a source of salt. The fisheries potential of Lake Kivu is more limited than that of the other lakes of the Western Rift, but a large quantity of natural gas is obtained from the lake each year. Tourist attractions are available, and, at the outlet of the lake below Bukavu, Congo, a hydroelectric station on the Ruzizi River provides power to the Burundi capital of Bujumbura on the northern shores of Lake Tanganyika. Lake Tanganyika near Bujumbura, Burundi As a whole, the borderlands of Lake Tanganyika are characterized by underdevelopment (see photograph, although peasant fishermen operate in the northern part of the lake, where fisheries are dominated by the exploitation of dagaa. There is a secondary output from other species, but in the absence of shallow, marginal waters Tilapia do not form a significant proportion of the catch. Despite the changes in water level to which it is liable and its remoteness from markets, Lake Rukwa is third to Lakes Victoria and Tanganyika among the freshwater fisheries of Tanzania. In the northern waters of Lake Nyasa the fish caught include catfish and some species of carp, whereas in the southern part of the lake shallow, sheltered waters provide a good habitat for Tilapia and for Labeo mesops (a species of carp). The majority of the fishermen also practice subsistence agriculture, except on Likoma Island. Commercial fishing, however, has intensified the demand upon the inshore species, resulting in a reduction of the fish population.