{{#invoke:Other uses|otherX|places with the same name}} Template:Multiple issues Template:Short description Template:Use dmy dates Template:Infobox body of water
Lake Victoria is one of the African Great Lakes. With a surface area of approximately Template:Cvt,<ref>Template:Cite journal</ref><ref name="auto3">Template:Cite bookTemplate:Full</ref>Template:Page needed Lake Victoria is Africa's largest lake by area, the world's largest tropical lake,<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> and the world's second-largest fresh water lake by surface area after Lake Superior in North America.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> In terms of volume, Lake Victoria is the world's ninth-largest continental lake, containing about Template:Cvt of water.<ref name="auto3"/><ref name="auto4">Template:Cite journal</ref> Lake Victoria occupies a shallow depression in Africa. The lake has an average depth of Template:Cvt and a maximum depth of Template:Cvt.<ref name="auto3"/><ref name="auto4"/><ref name="UNEP99">United Nations, Development and Harmonisation of Environmental Laws Volume 1: Report on the Legal and Institutional Issues in the Lake Victoria Basin, United Nations, 1999, page 17</ref> Its catchment area covers Template:Cvt.<ref>Template:Cite journal</ref> The lake has a shoreline of Template:Cvt when digitized at the 1:25,000 level,<ref>Template:Cite bookTemplate:Full</ref>Template:Page needed with islands constituting 3.7% of this length.<ref name="Hickling61">Template:Cite bookTemplate:Full</ref>Template:Page needed
The lake's area is divided among three countries: Tanzania occupies 49% (Template:Cvt), Uganda 45% (Template:Cvt), and Kenya 6% (Template:Cvt).<ref>J. Prado, R.J. Beare, J. Siwo Mbuga & L.E. Oluka, 1991. A catalogue of fishing methods and gear used in Lake Victoria. UNDP/FAO Regional Project for Inland Fisheries Development (IFIP), FAO RAF/87/099-TD/19/91 (En). Rome, Food and Agricultural Organization.</ref>
The lake is home to many species of fish which live nowhere else, especially cichlids. Invasive fish, such as the Nile perch, have driven many endemic species to extinction.
NamesEdit
Though having multiple local language names (Template:Langx; Template:Langx; Template:Langx; Template:Langx),<ref name="WDL1">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> the lake was renamed after Queen Victoria by the explorer John Hanning Speke, the first Briton to document it in 1858, while on an expedition with Richard Francis Burton.<ref>Template:Cite news</ref><ref>Template:Cite bookTemplate:Full Information is drawn from Part One, Chapters 1–7 (pp. 9–134).Template:Page needed</ref>Template:Page needed
GeologyEdit
Photojournalist John Reader, writing in his Alan Paton Literary Award-winning Africa: A Biography of a Continent,<ref>Template:Cite news</ref> describes Lake Victoria as being relatively geologically young at about 400,000-years old—having been formed as westward-flowing rivers were backed up "when a fractured block of the Earth's crust tilted along the line of the Great Rift Valley, raising its western edge".<ref name="Reader">Template:Cite book</ref>Template:Better source A primary study, attempting "fluvial differentiation of the basin of Lake Victoria", draws several relevant tentative conclusions. First, during the Miocene era, what is now the catchment area of the lake was on the western side of an uplifted area that functioned as a continental divide, with streams on the western side flowing into the Congo River basin and streams on the eastern side flowing to the Indian Ocean. Second, as the East African Rift System formed, the eastern wall of the Albertine Rift (or Western Rift) rose, gradually reversing the drainage towards what is now Lake Victoria. Third, the opening of the main East African Rift and the Albertine Rift downwarped the area between them as the rift walls rose, creating the current Lake Victoria basin.<ref>Template:Cite journalTemplate:Primary source inline</ref>Template:Primary source inline
During its geological history, Lake Victoria went through changes ranging from its present shallow depression, through to what may have been a series of much smaller lakes.<ref name="Hickling61"/>Template:Page neededTemplate:Update after Geological cores taken from its bottom show Lake Victoria has dried up completely at least three times since it formed.<ref name="Reader"/>Template:Better source These drying cycles are probably related to past ice ages, which were times when precipitation declined globally.<ref name="Reader"/>Template:Better source According to another primary source, Lake Victoria last dried out about 17,300 years ago, and it refilled 14,700 years ago<ref name="Verheyen2003">Template:Cite journal</ref>Template:Primary source inline—as the African humid period began.<ref>Template:Cite journal</ref>
Hydrology and limnologyEdit
Lake Victoria receives 80 percent of its water from direct rainfall.<ref name="Hickling61"/>Template:Page needed Average evaporation on the lake is between Template:Convert per year, almost double the precipitation of riparian areas.<ref>Template:Cite book</ref> Lake Victoria receives its water additionally from rivers, and thousands of small streams. The Kagera River is the largest river flowing into this lake, with its mouth on the lake's western shore. Lake Victoria is drained solely by the Nile River near Jinja, Uganda on the lake's northern shore.<ref name="Fishery">Template:Cite book</ref>
Template:More citations needed In the Kenya sector, the main influent rivers are the Sio, Nzoia, Yala, Nyando, Sondu Miriu, Mogusi, and Migori. The only outflow from Lake Victoria is the Nile River, which exits the lake near Jinja, Uganda. In terms of contributed water, this makes Lake Victoria the principal source of the longest branch of the Nile. However, the most distal source of the Nile Basin, and therefore the ultimate source of the Nile, is more often considered to be one of the tributary rivers of the Kagera River (the exact tributary remains undetermined), and which originates in either Rwanda or Burundi. The uppermost section of the Nile is generally known as the Victoria Nile until it reaches Lake Albert. Although it is a part of the same river system known as the White Nile and is occasionally referred to as such, strictly speaking this name does not apply until after the river crosses the Uganda border into South Sudan to the north.
The lake exhibits eutrophic conditions. In 1990–1991, oxygen concentrations in the mixed layer were higher than in 1960–1961, with nearly continuous oxygen supersaturation in surface waters. Oxygen concentrations in hypolimnetic waters (i.e., the layer of water that lies below the thermocline, is noncirculating, and remains perpetually cold) were lower in 1990–1991 for a longer period than in 1960–1961, with values of less than 1 mg per litre (< 0.4 gr/cu ft) occurring in water as shallow as Template:Convert compared with a shallowest occurrence of greater than Template:Convert in 1961. The changes in oxygenation are considered consistent with measurements of higher algal biomass and productivity.<ref>Template:Cite journal</ref> These changes have arisen for multiple reasons: successive burning within its basin,<ref>Template:Cite journal</ref> soot and ash from which has been deposited over the lake's wide area; from increased nutrient inflows via rivers,<ref name="OchumbaKibaara">Template:Cite journal</ref> and from increased pollution associated with settlement along its shores.<ref>Template:Cite news</ref>
Between 2010 and 2022 the surface area of Lake Victoria increased by 15%<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> flooding lakeside communities.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
BathymetryEdit
The lake is a shallow lake considering its large geographic area with a maximum depth of approximately Template:Convert and an average depth of Template:Convert.<ref>Template:Cite journal</ref> A 2016 project digitized ten-thousand points and created the first true bathymetric map of the lake.<ref name=":0"/> The deepest part of the lake is offset to the east of the lake near Kenya and the lake is generally shallower in the west along the Ugandan shoreline and the south along the Tanzanian shoreline.<ref name=":0"/>
Native wildlifeEdit
MammalsEdit
Many mammal species live in the region of Lake Victoria, and some of these are closely associated with the lake itself and the nearby wetlands. Among these are the hippopotamus, African clawless otter, spotted-necked otter, marsh mongoose, sitatunga, bohor reedbuck, defassa waterbuck, cane rats, and giant otter shrew.<ref>Template:Cite bookTemplate:Full</ref>Template:Page needed
ReptilesEdit
Lake Victoria and its wetlands has a large population of Nile crocodiles, as well as African helmeted turtles, variable mud turtles, and Williams' mud turtle.<ref name="Spawls2002">Template:Cite bookTemplate:Full</ref>Template:Page needed The Williams' mud turtle is restricted to Lake Victoria and other lakes, rivers, and swamps in the upper Nile basin.<ref name="Spawls2002"/>Template:Page needed
Cichlid fishEdit
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Lake Victoria formerly was very rich in fish, including many endemics, but a high percentage of these became extinct since the 1940s.<ref name="Witte1992">Template:Cite journal</ref> The main group in Lake Victoria is the haplochromine cichlids (Haplochromis sensu lato) with more than 500 species, almost all endemic,<ref name="Verheyen2003"/><ref name="Meier2017">Template:Cite journal</ref><ref name="DeWeerdt2004">DeWeerdt, S. (28 February 2004). Dark secret of the lake. New Scientist. Retrieved 26 March 2017.</ref> and including an estimated 300 that still are undescribed.<ref name="Sayer2018">Sayer, C.A., L. Máiz-Tomé, and W.R.T. Darwall (2018). Freshwater biodiversity in the Lake Victoria Basin: Guidance for species conservation, site protection, climate resilience and sustainable livelihoods. Cambridge, UK and Gland, Switzerland: IUCN. {{#invoke:doi|main}}</ref> This is far more species of fish than any other lake in the world, except Lake Malawi.<ref name="Turner2001">Template:Cite journal</ref> These are the result of a rapid adaptive radiation in the last circa 15,000 years.<ref name="Verheyen2003"/><ref name="Meier2017"/><ref>Template:Cite journal</ref> Their extraordinary diversity and speed of evolution have been the subjects for many scientists studying the forces that drive the richness of life everywhere.<ref name="Meier2017"/><ref name="Lowe2009">Template:Cite journal</ref> The Victoria haplochromines are part of an older group of more than 700 closely related species, also including those of several smaller lakes in the region, notably Kyoga, Edward–George, Albert, and Kivu.<ref name="Verheyen2003"/><ref name="Meier2017"/>
Most of these lakes are relatively shallow (like Victoria) and part of the present-day upper Nile basin. The exception is Lake Kivu, which is part of the present-day Congo River basin, but is believed to have been connected to Lakes Edward and Victoria by rivers until the uplifting of parts of the East African Rift.<ref name="Verheyen2003"/> This deep lake may have functioned as an "evolutionary reservoir" for this haplochromine group in periods where other shallower lakes in the region dried out, as happened to Lake Victoria about 15,000 years ago.<ref name="Verheyen2003"/> In recent history only Lake Kyoga was easily accessible to Victoria cichlids, as further downstream movement by the Victoria Nile (to Lake Albert) is prevented by a series of waterfalls, notably Murchison. In contrast, the Owen Falls (now flooded by a dam) between Victoria and Kyoga were essentially a series of rapids that did not effectively block fish movements between the two lakes.<ref>McClanahan, T. and T.P. Young (1996). East African Ecosystems and Their Conservation. pp. 201–06. Template:ISBN</ref>
The Victoria haplochromines are distinctly sexually dimorphic (males relatively brightly colored; females dull),<ref>Template:Cite journal</ref> and their ecology is extremely diverse, falling into at least 16 groups, including detritivores, zooplanktivores, insectivores, prawn-eaters, molluscivores and piscivores.<ref name="Lowe2009"/> As a result of predation by the introduced Nile perch, eutrophication and other changes to the ecosystem, it is estimated that at least 200 species (about 40 percent) of Lake Victoria haplochromines have become extinct,<ref name="DeWeerdt2004"/><ref name="Lowe2009"/><ref name="Rijssel2013">Template:Cite journal</ref> including more than 100 undescribed species.<ref name="Sayer2018"/> Initially it was feared that this number was even higher, by some estimates 65 percent of the total species,<ref>Template:Cite journal</ref> but several species that were feared extinct have been rediscovered after the Nile perch started to decline in the 1990s.<ref name="Lowe2009"/><ref name="IUCNef">IUCN Red Lists: Geographic Patterns. Eastern Africa. Retrieved 25 March 2017.</ref> Several of the remaining species are seriously threatened and additional extinctions are possible.<ref name="Fiedler1998">Fiedler, P.L. and P M. Kareiva, editors (1998). Conservation Biology: For the Coming Decade. 2nd edition. pp. 209–10. Template:ISBN</ref> Some species have survived in nearby small satellite lakes,<ref name="IUCNef"/> have survived in refugias among rocks or papyrus sedges (protecting them from the Nile perch),<ref name="Chapman1996">Template:Cite journal</ref> or have adapted to the human-induced changes in the lake itself.<ref name="Lowe2009"/><ref name="Rijssel2013"/> Such adaptions include a larger gill area (adaption for oxygen-poor water), changes in the feeding apparatus, changes to the eyes (giving them better sight in turbid water)<ref name="Witte2000"/><ref name="Lowe2009"/> and smaller head/larger caudal peduncle (allowing faster swimming).<ref>Template:Cite journal</ref> The piscivorous (affected by both predation and competition from Nile perch<ref>Template:Cite journal</ref>), molluscivorous and insectivorous haplochromines were particularly hard hit with many extinctions.<ref name="Lowe2009"/> Others have become extinct in their pure form, but survive as hybrids between close relatives (especially among the detritivores).<ref name="DeWeerdt2004"/><ref name="Lowe2009"/> The zooplanktivores have been least affected and in the late 1990s had reached densities similar to, or above, the densities before the drastic declines, although consisting of fewer species and often switching their diet towards macroinvertebrates.<ref name="Witte2000"/><ref name="Lowe2009"/> Some of the threatened Lake Victoria cichlid species have captive "insurance" populations in zoos, public aquaria and among private aquarists, and a few species are extinct in the wild (only survive in captivity).<ref>Yirka, B. (27 November 2015). Study shows evolution does not always mean more diversification. Phys.org, press release. Retrieved 28 March 2017.</ref><ref>Lévêque, C. (1997). Biodiversity Dynamics and Conservation: The Freshwater Fish of Tropical Africa. p. 358. Template:ISBN</ref><ref>Steeves, G: "New to the hobby Haplochromines". Cichlid-Forum. Retrieved 28 March 2017.</ref><ref>Rizza, D: "Looking At Victoria Cichlids". Conscientious Aquarist Magazine. Retrieved 28 March 2017.</ref><ref>McAndrews, R. and D.I. Warmolts (25 May 2015). "Progress in breeding freshwater fish". Boston Aquarium Society. Retrieved 14 April 2017.</ref>
Before the mass extinction that has occurred among the lake's cichlids in the last 50 years, about 90 percent of the native fish species in the lake were haplochromines.<ref name="Witte1992"/> Disregarding the haplochromines, the only native Victoria cichlids are two critically endangered tilapia, the Singida tilapia or ngege (Oreochromis esculentus) and Victoria tilapia (O. variabilis).<ref>Template:Cite iucn</ref><ref>Template:Cite iucn</ref>
In 1927–1928 Michael Graham conducted the first ever systematic Fisheries Survey of Lake Victoria. In his official report of the expedition, Graham wrote that "The ngege or satu Tilapia esculenta, is the most important food fish of the lake, whether for native or non-native consumption. No other fish equals it in the quality of the flesh. It is convenient size for trade, travels well and is found in much greater numbers than other important fish, such as semutundu (Luganda), Bagrus sp.".<ref name=":25">Graham M. (1929.) The Victoria Nyanza and Its Fisheries: A Report on the Fish Survey of Lake Victoria 1927–1928 and Appendices. London: Crown Agents for the Colonies. 256pp.</ref> Furthermore, Graham noted that the introduction of the European flax gill net of 5 inch mesh had undoubtedly caused a diminution in the number of ngege in those parts of the Kavirondo Gulf, the northern shore of the lake, the Sesse Islands and Smith's Sound which are conveniently situated close to markets.<ref name=":25"/> Survey catches in 1927–28 included several Haplochromis species that are now thought to be extinct, including: Haplochromis flavipinnis, Haplochromis gowersii, Haplochromis longirostris, Haplochromis macrognathus, Haplochromis michaeli, Haplochromis nigrescens, Haplochromis prognathus.
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As well as being due to the introduction of Nile perch, the extinction of cichlids in the genus Haplochromis has also been blamed on the lake's eutrophication. The fertility of tropical waters depends on the rate at which nutrients can be brought into solution. The influent rivers of Lake Victoria provide few nutrients to the lake in relation to its size. Because of this, most of Lake Victoria's nutrients are thought to be locked up in lake-bottom deposits.<ref name="Hickling61" />Template:Page needed<ref name="Beauchamp54">Template:Cite journal</ref> By itself, this vegetative matter decays slowly. Animal flesh decays considerably faster, however, so the fertility of the lake is dependent on the rate at which these nutrients can be taken up by fish and other organisms.<ref name="Beauchamp54" /> There is little doubt that Haplochromis played an important role in returning detritus and plankton back into solution.<ref name="Lucy Richardson">Template:Citation</ref><ref name="KaufmanOchumba93">Template:Cite journal</ref><ref name="Goldschmidt93">Template:Cite journal</ref> With some 80 percent of Haplochromis species feeding off detritus, and equally capable of feeding off one another, they represented a tight, internal recycling system, moving nutrients and biomass both vertically and horizontally through the water column, and even out of the lake via predation by humans and terrestrial animals. The removal of Haplochromis, however, may have contributed to the increasing frequency of algal blooms,<ref name="OchumbaKibaara" /><ref name="KaufmanOchumba93" /><ref name="Goldschmidt93" /> which may in turn be responsible for mass fish kills.<ref name="OchumbaKibaara" />
Other fishEdit
The non-cichlid native fish include African tetras (Brycinus), cyprinids (Enteromius, Garra, Labeo, Labeobarbus, Rastrineobola and Xenobarbus), airbreathing catfish (Clariallabes, Clarias and Xenoclarias), bagrid catfish (Bagrus), loach catfish (Amphilius and Zaireichthys), silver butter catfish (Schilbe intermedius), Synodontis squeaker catfish, Nothobranchius killifish, poeciliids (Aplocheilichthys and Micropanchax), the spiny eel Mastacembelus frenatus, elephantfish (Gnathonemus, Hippopotamyrus, Marcusenius, Mormyrus, Petrocephalus, and Pollimyrus), the climbing gourami Ctenopoma muriei and marbled lungfish (Protopterus aethiopicus).<ref name="FishBaseList">FishBase: Fish Species in Victoria. Retrieved 25 March 2017.</ref>
At a genus level, most of these are widespread in Africa, but the very rare Xenobarbus and Xenoclarias are endemic to the lake, and the common Rastrineobola is near-endemic.<ref name="FishBaseList"/>
CrustaceansEdit
Four species of freshwater crabs are known from Lake Victoria: Potamonautes niloticus is widespread in the lake and P. emini has been recorded from the vicinity of Bukoba in Tanzania, but both are also found elsewhere in Africa.<ref>Cumberlidge, N. (2009). "Freshwater Crabs and Shrimps (Crustacea: Decapoda) of the Nile Basin". Chapter 27, pp. 547–61 in : Dumony, H.J. (editor). The Nile. Origin, Environments, Limnology and Human Use. Monographiae Biologicae, Vol. 89. Springer, New York. Template:ISBN.</ref><ref>Template:Cite iucn</ref> The last were first scientifically described in 2017 and very little is known about them: P. entebbe is only known from near Entebbe (the only known specimen was collected in 1955 and it is unknown if it was in or near the lake) and P. busungwe only at Busungwe Island in the northwestern part of the lake. The latter likely is the smallest African freshwater crab with a carapace width up to about Template:Cvt, although P. kantsyore of Kagera River, and Platythelphusa maculata and P. polita of Lake Tanganyika are almost as small.<ref>Template:Cite journal</ref>
The only shrimp/prawn is Caridina nilotica,<ref>Template:Cite journal</ref> which is common and widespread in Lake Victoria.<ref name="Lowe2009"/>
MolluscsEdit
Lake Victoria is home to 28 species of freshwater snails (e.g., Bellamya, Biomphalaria, Bulinus, Cleopatra, Gabbiella, and Melanoides), including 12 endemic species/subspecies.<ref name="Darwall2011">Template:Cite book</ref><ref>Brown, D. (1994). Freshwater Snails of Africa and Their Medical Importance. 2nd edition. Template:ISBNTemplate:Full</ref>Template:Page needed There are 17 species of bivalves (Corbicula, Coelatura, Sphaerium, and Byssanodonta), including 6 endemic species and subspecies.<ref name="Darwall2011"/><ref>Template:Cite journal</ref> It is likely that undescribed species of snails remain. Conversely, genetic studies indicate that some morphologically distinctive populations, traditionally regarded as separate species, may only be variants of single species.<ref name="Sayer2018"/> Two of the snail genera, Biomphalaria and Bulinus, are intermediate hosts of the parasite that causes bilharzia (schistosomiasis). Human infections by this parasite are common at Lake Victoria.<ref>Template:Cite news</ref> This may increase as a result of the spread of the invasive water hyacinth (an optimum snail habitat),<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> and the loss of many snail-eating cichlids in the lake.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
SpidersEdit
Evarcha culicivora is a species of jumping spider (family Salticidae) found only around Lake Victoria in Kenya and Uganda. It feeds primarily on female mosquitos.<ref>Template:Cite journal</ref>
FisheriesEdit
{{#invoke:Labelled list hatnote|labelledList|Main article|Main articles|Main page|Main pages}} Lake Victoria supports Africa's largest inland fishery (as of 1997).<ref name="Geheb97">Template:Cite thesis</ref> Initially the fishery involved native species, especially tilapia and haplochromine cichlids, but also catfish (Bagrus, Clarias, Synodontis and silver butter catfish), elephantfish, ningu (Labeo victorianus) and marbled lungfish (Protopterus aethiopicus).<ref name="LVFO2016">Lake Victoria Fisheries Organization (2016). {{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name="Njiru2005">Template:Cite journal</ref> Some of these, including tilapia and ningu (Labeo victorianus), had already declined in the first half of the 20th century due to overfishing.<ref name="Lowe2009"/><ref>Template:Cite iucn</ref> To boost fishing, several species of non-native tilapia and Nile perch were introduced to the lake in the 1950s. Nevertheless, the natives continued to dominate fisheries until the 1970s where their decline meant that there was a strong shift towards the non-native Nile tilapia (now 7 percent of catches), non-native Nile perch (60 percent) and the native Lake Victoria sardine (30 percent).<ref name="Lowe2009"/><ref name="Njiru2005"/> Because of its small size, the abundant open-water Lake Victoria sardine only supported minor fisheries until the decline of other natives.<ref name="Njiru2005"/> At the peak in the early 1990s, Template:Convert of Nile perch were landed annually in Lake Victoria, but this has declined significantly in later years.<ref name="Lowe2009"/>
Environmental issuesEdit
A number of environmental issues are associated with Lake Victoria and the complete disappearance of many endemic cichlid species has been called the "most dramatic example of human-caused extinctions within an ecosystem".<ref name="Fiedler1998"/>
Invasive fishEdit
Starting in the 1950s, many species have been introduced to Lake Victoria where they have become invasive and a prime reason for the extinction of many endemic haplochromine cichlids.<ref name="Witte1992"/> Among the introductions are several tilapias: redbreast (Coptodon rendalli), redbelly (C. zillii), Nile (Oreochromis niloticus) and blue-spotted tilapias (O. leucostictus).<ref name="Lowe2009"/><ref name="Njiru2005"/><ref name="Pringle2005">Pringle, R.M. (2005). The Origins of the Nile Perch in Lake Victoria. BioScience 55 (9): 780–787.</ref> Although these have contributed to the extinction of native fish by causing significant changes to the ecosystem, outcompeted natives and (in the case of the Nile tilapia) possibly hybridized with the highly threatened native tilapias, the most infamous introduction was the large and highly predatory Nile perch (Lates niloticus).<ref name="Witte1992"/><ref name="Lowe2009"/><ref name="Njiru2005"/>
As early as the 1920s, it was proposed to introduce a large pelagic predator such as the Nile perch to improve the fisheries in the lake. At the same time it was warned that this could present a serious danger to the native fish species and required extensive research into possible ecological effects before done.<ref name="Pringle2005"/> These warnings primarily concerned the native tilapia O. esculentus, as the smaller haplochromine cichlids (despite playing an important role in local fisheries) were regarded as "trash fish" by the colonial government.<ref name="Pringle2005"/> In the following decades, the pressure to introduce the Nile perch continued, as did warnings about the possible effects of doing it.<ref name="Pringle2005"/> The first introduction of Nile perch to the region, done by the Uganda Game and Fisheries Department (then part of the colonial government) and local African fish guards, happened upstream of Murchison Falls directly after the completion of the Owen Falls Dam in 1954. This allowed it to spread to Lake Kyoga where additional Nile perch were released in 1955, but not Victoria itself.<ref name="Pringle2005"/> Scientists argued that further introduction should wait until research showed the effect of the introduction in Kyoga, but by the late 1950s, Nile perch began being caught in Lake Victoria.<ref name="Pringle2005"/> As the species was already present, there were few objections when more Nile perch were transferred to Victoria to further bolster the stock in 1962–63.<ref name="Pringle2005"/>
The origin of the first Victoria introductions in the 1950s is not entirely clear and indisputable evidence is lacking. Uganda Game and Fisheries Department (UGFD) officials denied that they were involved, but circumstantial evidence suggests otherwise and local Africans employed by UGFD have said that they introduced the species in 1954–55 under the directive of senior officials.<ref name="Pringle2005"/> UGFD officials argued that Nile perch must have spread to Lake Victoria by themselves by passing through the Owen Falls Dam when shut down for maintenance, but this is considered highly unlikely by many scientists.<ref name="Pringle2005"/> The Nile perch had spread throughout the lake by 1970.<ref name="Lowe2009"/> Initially the population of the Nile perch was relatively low, but a drastic increase happened, peaking in the 1980s, followed by a decline starting in the 1990s.<ref name="Lowe2009"/>
Due to the presence of the Nile perch, the natural balance of the lake's ecosystem has been disrupted. The food chain is being altered and in some cases, broken by the indiscriminate eating habits of the Nile perch. The subsequent decrease in the number of algae-eating fish allows the algae to grow at an alarming rate, thereby choking the lake. The increasing amounts of algae, in turn, increase the amount of detritus (dead plant material) that falls to the deeper portions of the lake before decomposing. As a by-product of this the oxygen levels in the deeper layer of water are being depleted. Without oxygen, any aerobic life (such as fish) cannot exist in the deeper parts of the lake, forcing all life to exist within a narrow range of depth. In this way, the Nile perch has degraded the diverse and thriving ecosystem that was once Lake Victoria. The abundance of aquatic life is not the only dependent of the lake: more than thirty million people in Tanzania, Kenya and Uganda rely on the lake for its natural resources.
Hundreds of endemic species that evolved under the special conditions offered by the protection of Lake Victoria have been lost due to extinction, and several more are still threatened.<ref>Template:Cite journal</ref> Their loss is devastating for the lake, the fields of ecology, genetics and evolution biology, and more evidently, for the local fisheries. Local fisheries once depended on catching the lungfish, tilapia, carp and catfish that comprise the local diet. Today, the composition and yields of such fish catches are virtually negligible. Extensive fish kills, Nile perch, loss of habitat and overfishing have caused many fisheries to collapse and many protein sources to be unavailable at the market for local consumption. Few fisheries, though, have been able to make the switch to catching the Nile perch, since that requires a significant amount of capital resources.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
Water hyacinth invasionEdit
{{#invoke:Labelled list hatnote|labelledList|Main article|Main articles|Main page|Main pages}}
The water hyacinth has become a major invasive plant species in Lake Victoria.
The release of large amounts of untreated wastewater (sewage) and agricultural and industrial runoff directly into Lake Victoria over the past 30 years has greatly increased the nutrient levels of nitrogen and phosphorus in the lake "triggering massive growth of exotic water hyacinth, which colonised the lake in the late 1990s".<ref name="Luilo">Luilo, G.B. (August 01, 2008). Lake Victoria water resources management challenges and prospects: a need for equitable and sustainable institutional and regulatory frameworks African Journal of Aquatic Science 33, 2, 105–13.</ref><ref>Template:Cite journal</ref> This invasive weed creates anoxic (total depletion of oxygen levels) conditions in the lake, inhibiting decomposing plant material, raising toxicity and disease levels to both fish and people. At the same time, the plant's mat or "web" creates a barrier for boats and ferries to maneuver, impedes access to the shoreline, interferes with hydroelectric power generation, and blocks the intake of water for industries.<ref name="Luilo"/><ref name="Kateregga, E. & Sterner, T.">Kateregga, E., & Sterner, T. (January 01, 2009). "Lake Victoria Fish Stocks and the Effects of Water Hyacinth". Journal of Environment & Development, 18, 1, 62–78.</ref><ref>Mailu, A.M., G.R.S. Ochiel, W. Gitonga and S.W. Njoka. 1998. Water Hyacinth: An Environmental Disaster in the Winam Gulf of Lake Victoria and its Control, pp. 101–05.</ref><ref>Template:Cite journal</ref><ref name="Albright2004">Albright, T.P., Moorhouse, T.G., & McNabb, T.J. (January 1, 2004). "The Rise and Fall of Water Hyacinth in Lake Victoria and the Kagera River Basin, 1989-2001". Journal of Aquatic Plant Management, 42, 73–84.</ref> On the other hand, water hyacinth mats can potentially have a positive effect on fish life in that they create a barrier to overfishing and allow for fish growth, there has even been the reappearance of some fish species thought to have been extinct in recent years. The overall effects of the water hyacinth, however, are still unknown.<ref name="Kateregga, E. & Sterner, T."/><ref>Jäger, J., Bohunovsky, L., Radosh, L., & Sustainability Project. (2008). Our planet: How much more can earth take?. London: Haus.</ref>
Growth of the water hyacinth in Lake Victoria has been tracked since 1993, reaching its maxima biomass in 1997 and then declining again by the end of 2001.<ref name="Kateregga, E. & Sterner, T."/> Greater growth was observed in the northern part of the lake, in relatively protected areas, which may be linked to current and weather patterns and could also be due to the climate and water conditions, which are more suitable to the plants growth (as there are large urban areas to the north end of the lake, in Uganda).<ref name="Albright2004"/> The invasive weed was first attempted to be controlled by hand, removed manually from the lake; however, re-growth occurred quickly. Public awareness exercises were also conducted.<ref name="Albright2004"/> More recently, measures have been used such as the introduction of natural insect predators, including two different water hyacinth weevils and large harvesting and chopping boats, which seem to be much more effective in eliminating the water hyacinth.<ref name="Albright2004"/><ref>Ochiel, G.S., A.M. Mailu, W. Gitonga and S.W. Njoka. 1999. Biological Control of Water Hyacinth on Lake Victoria, Kenya, pp. 115–18.</ref><ref>Mallya, G.A. 1999. Water hyacinth control in Tanzania, pp. 25–29.</ref><ref>United Nations Environment Programme & Belgium. (2006). Africa's lakes: Atlas of our changing environment. Nairobi, Kenya: UNEP.</ref> A green power plant that uses harvested water hyacinth (but also can use other degradable waste) was constructed in Kisumu County in 2013. In addition to the biogas it produces, its by-product can be used as fertilizer.<ref name="Sayer2018"/>
Other factors which may have contributed to the decline of the water hyacinth in Lake Victoria include varying weather patterns, such as El Niño during the last few months of 1997 and first six months of 1998 bringing with it higher levels of water in the lake and thus dislodging the plants. Heavy winds and rains along with their subsequent waves may have also damaged the plants during this same time frame. The plants may not have been destroyed, instead merely moved to another location. Additionally, the water quality, nutrient supply, temperature, and other environmental factors could have played a role. Overall, the timing of the decline could be linked to all of these factors and perhaps together, in combination, they were more effective than any one deterrent would have been by itself.<ref name="Albright2004"/> The water hyacinth is in remission and this trend could be permanent if control efforts are continued.<ref>Crisman, T.L., Chapman, Lauren J., Chapman, Colin A., & Kaufman, Les S. (2003). Conservation, ecology, and management of African fresh waters. Gainesville: University Press of Florida.</ref>
PollutionEdit
Pollution of Lake Victoria is mainly due to discharge of raw sewage into the lake, dumping of domestic and industrial waste, and fertiliser and chemicals from farms.
The Lake Victoria basin, while generally rural, has many major centres of population. Its shores are dotted with key cities and towns, including Kisumu, Kisii, and Homa Bay in Kenya; Kampala, Jinja and Entebbe in Uganda; and Bukoba, Mwanza, and Musoma in Tanzania. These cities and towns are also home to many factories that discharge some chemicals directly into the lake or its influent rivers. The set up of small beaches and local authorities around the lake lack proper sewage treatment facilities allowing pollutants to find their way into the water.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>Template:Cite journal</ref> Large parts of these urban areas also discharge untreated (raw) sewage into the river, increasing its eutrophication that in turn is helping to increase the invasive water hyacinth.<ref name="earthobservatory.nasa.gov">Template:Cite news</ref> Increased logging and act of deforestation has led to environmental degradation around the region reducing the absorption of polluting chemicals and deteriorating the water quality.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
Environmental dataEdit
As of 2016, an environmental data repository exists for Lake Victoria.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The repository contains shoreline, bathymetry, pollution, temperature, wind vector, and other important data for both the lake and the wider Basin.
History and explorationEdit
The first recorded information about Lake Victoria comes from Arab traders plying the inland routes in search of gold, ivory, other precious commodities, and slaves.
The lake existed and was known to many Africans in the catchment area who left no written records long before it was sighted by a European in 1858 when the British explorer John Hanning Speke reached its southern shore while on his journey with Richard Francis Burton to explore central Africa and locate the Great Lakes. Believing he had found the source of the Nile on seeing this "vast expanse of open water" for the first time, Speke named the lake after Queen Victoria. Burton, who had been recovering from illness at the time and resting further south in Kazeh (near present-day Tabora),<ref>Template:Cite bookTemplate:Full</ref>Template:Page needed was outraged that Speke claimed to have proved his discovery to have been the true source of the Nile River, which Burton regarded as still unsettled. A very public quarrel ensued, which not only sparked a great deal of intense debate within the scientific community of the day, but also much interest by other explorers keen to either confirm or refute Speke's discovery.<ref name = "DNB">Template:DNB Cite</ref>
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In the late 1860s, the famous Scottish explorer and missionary David Livingstone failed in his attempt to verify Speke's discovery, instead pushing too far west and entering the River Congo system instead.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Ultimately, the Welsh-American explorer Henry Morton Stanley, on an expedition funded by the New York Herald newspaper, confirmed the truth of Speke's discovery, circumnavigating the lake and reporting the great outflow at Ripon Falls on the lake's northern shore.
Water useEdit
Many towns and cities are reliant on Lake Victoria for their water supplies, for farming and other uses.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
Lamadi water schemeEdit
The Lamadi water scheme is a water and sanitation project that serves Mwanza and the satellite towns of Lamadi, Misungwi, Magu, Bukoba, and Musoma on the bank of Lake Victoria. European Investment Bank started the project in 2013 with the aim of protecting the environmental health of the lake, through improved water and sanitation to the towns whose pollution is part of the degradation of the lake. The project aims to provide safe drinking water for an estimated one million people and improved sanitation for 100 000 people. Sediment and suspended solids are filtered out using sand, which acts like a sieve. The water is then ready to be chlorinated or treated in another way. The sand filtration helps reduce water-borne diseases and is based on the use of the local environment.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
Nalubaale DamEdit
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The only outflow for Lake Victoria is at Jinja, Uganda, where it forms the Victoria Nile. The water for at least 12,000 years has drained across a natural rock weir. In 1952, engineers acting for the government of Colonial Uganda blasted out the weir and reservoir to replace it with an artificial barrage to control the level of the lake and reduce the gradual erosion of the rock weir. A standard for mimicking the old rate of outflow called the "agreed curve" was established, setting the maximum flow rate at 300 to 1,700 cubic metres per second (392–2,224 cu yd/sec) depending on the lake's water level.
In 2002, Uganda completed a second hydroelectric complex in the area, the Kiira Hydroelectric Power Station, with World Bank assistance. By 2006, the water levels in Lake Victoria had reached an 80-year low, and Daniel Kull, an independent hydrologist living in Nairobi, Kenya, calculated that Uganda was releasing about twice as much water as is allowed under the agreement,<ref>Template:Cite journal</ref> and was primarily responsible for recent drops in the lake's level.
TransportEdit
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Since the 1900s, Lake Victoria ferries have been an important means of transport between Uganda, Tanzania, and Kenya. The main ports on the lake are Kisumu, Mwanza, Bukoba, Entebbe, Port Bell, and Jinja. Until 1963, the fastest and newest ferry, MV Victoria, was designated a Royal Mail Ship. In 1966, train ferry services between Kenya and Tanzania were established with the introduction of Template:MV and Template:MV. The ferry MV Bukoba sank in the lake on 21 May 1996 with a loss of between 800 and 1,000 lives, making it one of Africa's worst maritime disasters.<ref>Template:Cite news</ref> Another tragedy occurred recently on 20 September 2018 that involved the passagers ferry MV Nyerere from Tanzania that caused the deaths of over 200 people.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
On 6 November 2022, Lake Victoria was the site of a commercial passenger aircraft crash. Precision Air Flight 494 an ATR 42–500 carrying 39 passengers and four crew, crashed while approaching Bukoba Airport, resulting in 19 fatalities.<ref>Template:Cite news</ref><ref>Template:Cite news</ref>
See alsoEdit
ReferencesEdit
External linksEdit
Template:Sister project Template:EB1911 Poster
- Decreasing levels of Lake Victoria Worry East African Countries
- New Scientist article Template:Webarchive on Uganda's violation of the agreed curve for hydroelectric water flow.
- Dams Draining Lake Victoria Template:Webarchive
- A Naturalist on Lake Victoria, with an Account of Sleeping Sickness and the Tse-tse Fly (1920). T.F. Unwin Ltd, London; Biodiversity Archive
- Video of Lake Victoria
- Institutions of the East African Community: Lake Victoria Fisheries Organisation
Template:African Great Lakes Template:Lakes of Tanzania Template:Lakes of Kenya Template:Hydrography of Uganda