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Lake Victoria: The Biggest Lake in Africa
Lake Victoria Information and Facts
Lake Victoria (or Victoria Nyanza in the Bantu language) is the largest of the African Great Lakes, the largest lake in Africa and the world’s second largest freshwater lake by surface area, after Lake Superior. It is crossed by the equator.
The lake has a surface area of 68,800 square kilometers (or 26,600 square miles), which also makes it the world’s largest tropical lake. By volume, the lake is the the ninth largest continental lake in the world, boasting around 2,750 cubic kilometers of water. It is the main source of freshwater for the big rural population living in its vicinity. Together with Lake Kyoga and Lake Albert, it forms a reservoir of 3,200 cubic kilometers of freshwater.
Lake Victoria has a maximum depth of 84 meters (or 276 feet), with an average depth of 40 meters (or 130 feet). The lake’s catchment area covers 184,000 square kilometers (or 71,040 square miles), and it has a shoreline of 4,828 kilometers (3,000 miles). Islands contribute to 3.7% of the total shore length.
The lake is located in 3 countries: Kenya has 6% of the total area (4,100 square kilometers or 1,600 square miles), Uganda has 45% (31,000 square kilometers or 12,000 square miles), and Tanzania has 49% (33,700 square kilometers or 13,000 square miles).
Hydrology and Geography
Precipitation contributes with 80% of Lake Victoria’s water. Lake evaporation measures between 2 and 2.2 meters (or 6.6 to 7.2 feet) every year.
Changes in the water balance of Lake Victoria are of major importance to several countries in the region, including Sudan and Egypt, which receive water from the Upper Nile basin. In addition to damage to Kenya, Uganda, and Tanzania, fluctuations in lake levels also affect Egypt, a densely populated country totally dependent on the continued flow of its largest river for drinking water and for power generation.
Lake Victoria has thousands of small inflowing streams. Its most important inflows are on the Kenyan part of the lake: Nzoya (257 kilometers), Yala, Sio, Sondu Miriu, Nyando, Migori, and Mogusi. All these Kenyan rivers contribute with far more water to the lake than the biggest tributary, the Kagera River, which flows into the lake on its western side.
Source of the Nile
Lake Victoria has one important outflow, the Nile River. The great African river exists the lake in Uganda, near Jinja. It then flows through the Lakes Kyoga and Albert and contributes on average with 14% of the flow in the combined White and Blue Niles as measured at Aswan. This makes Lake Victoria the main source of water for the longest branch of the Nile, although Lake Victoria itself is not considered the most distal source of the Nile. It should come as no surprise then that the uppermost section of the Nile, until the great river reaches Lake Albert, is also known as the Victoria Nile. The flow of the Nile is relatively constant due to the natural regulatory effect of the three equatorial lakes.
Shores and Islands
The shores of the lake are very varied. Steep rocks up to 90 meters (300 feet) high back the southwestern coast, while the western shore is marked by swamps, papyrus, which make way for the delta of the Kagera River. Lake Victoria’s northern coast is flat.
The Kavirondo Gulf has an average width of 25 kilometers (16 miles) and extends for 64 kilometers (40 miles) east of Kisumu in Kenya. The cities of Kampala and Entebbe are located on the lake’s northern coast.
Speke Gulf is located at the southeastern corner, while Emin Pasha Gulf is located at the southwestern corner. The lake also has many islands, among which Ukerewe is the largest. Ukerewe Island is located north of Speke Gulf, is densely populated, and has wooded hills that rise 200 meters (650 feet) above the lake. The Sese archipelago, comprising 62 islands, is located at the northwestern corner of the lake. Some of these islands are of incredible beauty.
Lake Victoria exhibits eutrophication (the enrichment of the lake with chemical nutrients). For example, in 1990-1991, oxygen levels in the mixed layer were higher than between 1960 and 1961, and there was almost continuous oxygen supersaturation in the upper layer.
Oxygen levels in hypolimnetic waters (the layer of water that is always cold and is noncirculating) were lower between 1990 and 1991 for a longer period of time than they were in 1960-1961. These changes in oxygenation are correlated with higher algal biomass and productivity, and have taken place for several reasons: burning in the lake’s basin (which caused ash and soot to be deposited on the lake’s great surface), more nutrients brought in by inflowing rivers, and increasing pollution levels.
Lake Victoria’s eutrophication is also considered the main culprit for the extinction of the Haplochromis cichlids. Fertility in tropical waters is greatly dependant on the rate at which nutrients are brought in, and Lake Victoria’s inflowing rivers are not great contributors of nutrients, especially taking into consideration the lake’s great size. This means that Lake Victoria’s nutrients are locked at the bottom of the lake, in deposits.
Haplochromis played a very important role in moving nutrients both vertically and horizontally in the water, and even out of it, via predation by animals. With around 80% of all Haplochromis species feeding off detritus, this meant that detritus and plankton were returned back into the solution. The extinction of Haplochromis is thought to have contributed to increased algal bloom frequencies, which in turn caused mass fish kills.
Lake Victoria is fills a shallow African depression, and went through many changes in its history. It’s thought that at one point it was a series of smaller lakes, and on at least 3 occasions the lake dried up completely. The times when the lake dried is thought to be linked to ice ages, when precipitation declined in the entire world.
The last time the lake dried was about 17,300 years ago, but it started refilling about 14,700 years ago. In geological terms, Lake Victoria is still pretty young, about 400,000 years old. It formed when an upthrown crustal block dammed westward-flowing rivers.
The lake’s geological history is probably the main contributor to its varied cichlid speciation. However, there are researchers who dispute this, arguing that the lake completely dried out sometime between 18,000 and 14,000 years ago, and there is no evidence of persisting ponds or marshes.
Lake Victoria is vulnerable to climate changes, because of its great surface area, its shallowness, and its limited inflow.
There are a number of environmental concerns associated with Lake Victoria, including invasive fish species and pollution.
Invasive Species: The Nile Perch Disaster
The Nile perch was introduced in the 1950s in order to increase fish harvests in the lake, although scientists were opposed to this. They believed that the Nile perch wouldn’t have a natural predator in the lake, which would destroy the lake’s ecosystem. However, the fish was clandestinely introduced into the lake in Uganda’s side of the lake in 1952. Later on, in 1962 and 1963, it was introduced intentionally. In 1964, the fish had already been recorded in Tanzania, in 1970 in Kenya, and by the early 1980s it was prevalent throughout the entire lake.
Now, in about 50 years since the introduction of the Nile perch, almost the entire natural and biological uniqueness and wealth of Lake Victoria is gone. The introduction of the Nile perch has driven several native cichlids to the brink of extinction. The lake used to host more than 350 endemic species of haplochromines, which were inspiring to scientists because of their incredible speed of evolution. Only a handful of species still struggle to exist today.
The presence of the Nile perch, which eats indiscriminately, has dramatically altered the balance of Lake Victoria’s ecosystem. The decrease in the numbers of algae-eating fish has caused the algae to grow at alarming rates. This, in turn, increases the amount of detritus which falls to the deeper parts of the lake before decomposing, which causes oxygen levels in deeper sections of the lake to plunge. Thus, aerobic life (like fish) can’t exist in the deeper parts of the lake.
The local fishing industry is also greatly affected by this. Lacking wood (which is used for drying the fish) and large processing plants that prepare the Nile perch for market, local fisheries can not be players on the Nile perch market. Additionally, traditional food sources that fisheries depended on like lungfish, tilapia, carp and catfishes are now negligible.
The population of the Nile Perch is also on course to dwindling over time. The fish used to have lots of food in the lake and often reached 240 kg by forcing itself, which caused extinctions among local populations of haplochromines. There are only a few available food sources remaining for the Nile perch, which means that the fish has resorted to cannibalism.
Hundreds of endemic species have gone extinct, and several are threatened. Their loss is devastating both for scientists working in ecology, evolution biology and genetics, but also for local fisheries.
Water Hyacinth Invasion
The invasion of the Water hyacinth has been caused by the release of sewage and agricultural or industrial runoff into Lake Victoria in the last 30 years. This led to a massive increase of nitrogen and phosphorus in the lake, which in turn resulted in the invasion of the Water hyacinth. The plant colonized the lake in the late 1990s, and is damaging because it depletes oxygen from the lake, thus raising toxicity and creating diseases in fish and people.
The plant’s web also creates barriers for ferries and boats, hinders hydroelectric power generation and the intake of water for industries. The plant can, however, also have a positive effect, by stopping overfishing and allowing fish growth. The Water hyacinth has been monitored since 1993, and it reached the maximum biomass in 1997. The northern part of the lake is more affected by the plant, because of weather patterns and water conditions, which are more favourable for the Water hyacinth due to the presence of large urban areas. Some of the methods of containment that have been tried include the introduction of insect predators and chopping boats, the latter of which are much more effective.
There are also good news though. The Water hyacinth is now in decline, due to several factors: the El Nino of the last months of 1997, heavy winds and high waves in the same timeframe, and water temperature. The remission could be permanent, if current control efforts are maintained.
The main pollution culprits in Lake Victoria include the discharge of raw sewage directly into the waters of the lake, industrial and domestic waste, and farm fertilisers and chemicals.
The area around the lake is one of the world’s most densely populated rural areas. Some of the most important towns and cities around the lake include: Kisumu (population: 410,000), Kisii (population: 200,000), and Homa Bay (population: 56,000) in Kenya; Kampala (population: 1.66 million), Entebbe (population: 80,000), and Jinja (population: 73,000) in Uganda; Mwanza (population: 707,000), Musoma (population: 134,000), and Bukoba (population: 86,000) in Tanzania.
The many factories and plants in these cities discharge their waste directly into Lake Victoria’s waters and the rivers that flow into it. The raw sewage that is being discharged also increases eutrophication, which sustains the Water hyacinth.
Fishing and fish processing have been and still are an important economic activity around Lake Victoria. The rapidly growing population in the lake’s basin heavily depends on fisheries as a source of protein. The introduction of gill nets in Lake Victoria in 1905 resulted in a gradual decline in the catches of endemic fish species, as observed in the period between 1905 and 1928.
The fishing effort was further increased in the 1940s when illegal undersized, mesh sizes were used. Nylon nets and outboard motors started being used in the 1950s. All these factors resulted in overfishing and a reduction in catches.
Exotic species were introduced into Lake Victoria, due to high demand for fish. These species include the tilapias Oreochromis nilotocis, O. leucostictus, Titlapia zillii, and T. remdalli (“melanopleaura”), along with the aforemoention Nile perch.
The introduced species resulted in increased commercial catches. In 1989, the lake produced over 500,000 tonnes of fish, predominantly Nile perch (63%), dagaa (Rastrineobola argentea) (19%), and Nile tilapia (9%).
The first map of Lake Victoria dates from the 1160s, and it was an accurate representation of the lake, which is also attributed as the source of the Nile. The map is called Al Idrisi map, after the calligrapher who created it. Arab traders searching for ivory and gold also provided the first pieces of information about the lake.
The British explorer John Hanning Speke is the first European who sighted the lake, on its southern shore, in 1858. Speke was in an expedition with Richard Francis Burton, an expedition aimed at exploring Central Africa and locating the Great Lakes.
Speke also believed that Lake Victoria was the source of the Nile, and named the lake after Queen Victoria. Burton was recovering from illness on the shores of Lake Tanganyika at the time, and was outraged at Speke’s claims to have found the source of the Nile.
David Livingstone was one of the explorers who failed to verify Speke’s claim, because he pushed too far West and entered the Congo River system. The truth of Speke’s claim was ultimately confirmed by Henry Morton Stanley, a Welsh-American explorer, who circumnavigated the lake and reported the great outflow on Lake Victoria’s northern shore.
Britain and Germany divided the lake at 1° South latitude in 1890, in the middle of European scramble for African colonies. The southern section was allotted to Germany, while the northern section to Britain. The Germans conducted important scientific projects on their section of the lake, for both strategic and research purposes.
Emil Pasha was a German doctor, naturalist and ornithologist. He stayed on the Nile north of Jinja for 12 years, and he used to send thousands of regional birds, animals and plants to museums in Europe. He founded the town of Bukoba in 1890, when he was on his way to his camp which was located near Lake Albert.
When he returned to Lake Albert, his camp was in total disorder. Going into the Congo, he was killed by a group of Arab slavers in 1892. The importance of his work is undeniable: he was the first pioneer naturalist who combined geographical exploration and scientific research in the fields of geology, biology, anthropology, and medicine.
Ferries have been operating on the lake since the 1900s, and have been a very important means of transportation between the 3 African countries located on the shores of Lake Victoria. Some of the most important ports are Mwanza, Kisumu, Entebbe, Bukoba, Jinja and Port Bell.
Until Kenya obtained its independence in 1963, the fastest and most modern ferry on the lake was MV Victoria, a Royal Mail Ship. Train ferry services were established between Tanzania and Kenya in 1966, when MV Umoja and MV Uhuru were introduced.
One of Africa’s worst maritime disasters happened on Lake Victoria on May 21st, 1996, when the ferry MV Bukoba sank, with a loss of lives estimated between 800 and 1,000.
The Owen Falls Dam, which later changed its name into the Nalubaale Dam, was completed in 1954, on the Victoria Nile at Jinja. It was part of a plan to gradually raise the level of the water in the lake. The dam turned the lake into a vast reservoir and provides hydroelectric power on a very large scale. A second dam, Kiira, located 1 kilometer (or 0.6 miles) away from Nalubaale, was completed in 1999. It began producing hydroelectric power in 2000.