Lake Victoria

Lake Victoria
Location	Africa
Coordinates	1°S 33°E / 1°S 33°E / -1; 33
Primary inflows	Kagera River
Primary outflows	White Nile (river) (known as the "Victoria Nile" as it flows out of the lake)
Catchment area	184,000 km2 (71,000 sq mi) 238,900 km2 (92,200 sq mi) basin
Basin countries	Tanzania Uganda Kenya
Max. length	337 km (209 mi)
Max. width	250 km (160 mi)
Surface area	68,800 km2 (26,600 sq mi)
Average depth	40 m (130 ft)
Max. depth	83 m (272 ft)
Water volume	2,750 km3 (660 cu mi)
Shore length1	3,440 km (2,140 mi)
Surface elevation	1,133 m (3,717 ft)
Islands	3,000 (Ssese Islands, Uganda)
Settlements	Bukoba, Tanzania Mwanza, Tanzania Musoma, Tanzania Kisumu, Kenya Kendu Bay, Kenya Homa Bay, Kenya Kampala, Uganda Entebbe, Uganda Jinja, Uganda
1 Shore length is not a well-defined measure.

Lake Victoria is one of the African Great Lakes. The lake was named after Queen Victoria of the United Kingdom, by John Hanning Speke, the first European to discover this lake.

With a surface area of 68,800 square kilometres (26,600 sq mi), Lake Victoria is Africa’s largest lake by area, and it is the largest tropical lake in the world. Lake Victoria is the world's second largest freshwater lake by surface area (only Lake Superior in North America is larger). In terms of its volume, Lake Victoria is the world's eighth largest continental lake, and it contains about 2,750 cubic kilometers (2.2 billion acre-feet) of water.

Lake Victoria receives most of its water from direct precipitation or from thousands of small streams. The largest stream flowing into this lake is the Kagera River, the mouth of which lies on the lake's western shore. There are two rivers that leave the lake, the White Nile (known as the "Victoria Nile" as it leaves the lake), flows out at Jinja, Uganda on the lake's north shore and the Katonga River flows out at Lukaya on the western shore connecting the lake to Lake George.^[1]

Lake Victoria occupies a shallow depression in Africa and has a maximum depth of 84 metres (276 ft) and an average depth of 40 metres (130 ft).^[2] Its catchment area covers 184,000 square kilometers (71,040 sq mi). The lake has a shoreline of 4,828 kilometres (3,000 mi), with islands constituting 3.7% of this length,^[3] and is divided among three countries: Kenya (6% or 4,100 km² (1,600 sq mi)^*), Uganda (45% or 31,000 km² (12,000 sq mi)^*) and Tanzania (49% or 33,700 km² (13,000 sq mi)^*).^[4]

Lake Victoria supports Africa's largest inland fishery.^[5]

Lake Victoria has, during its geological history, gone through changes ranging from its present shallow depression, through to what may have been a series of much smaller lakes.^[3] Geological cores taken from its bottom show that Lake Victoria has dried up completely at least three times since it formed.^[6] These drying cycles are probably related to past ice ages, which were times when precipitation declined globally.^[6] Lake Victoria last dried out 17,300 years ago, and it refilled beginning about 14,700 years ago. Geologically, Lake Victoria is relatively young – about 400,000 years old – and it formed when westward-flowing rivers were dammed by an upthrown crustal block.^[6]

This geological history probably contributed to the dramatic cichlid speciation that characterises its ecology, as well as that of other African Great Lakes,^[7] although there are researchers who dispute this, arguing that while Lake Victoria was at its lowest between 18,000 and 14,000 calendar years ago, and it dried out at least once during that time, there is no evidence of remnant ponds or marshes persisting within the desiccated basin. If such features existed, then they would have been small, shallow, turbid, and/or saline, and therefore markedly different from the lake to which today's species are adapted.^[8]

The shallowness of Lake Victoria, its limited river inflow, and its large surface area compared to its volume make it vulnerable to the effects of climate changes.

Lake Victoria receives almost all (80%) of its water from direct precipitation.^[3] Average evaporation on the lake is between 2–2.2 metres (6 ft 7 in – 7 ft 3 in) per annum, almost double the precipitation of riparian areas.^[9] In the Kenya Sector, the main influent rivers are the Sio, Nzoia, Yala, Nyando, Sondu Miriu, Mogusi and the Migori. Combined, these rivers contribute far more water to the lake than does the largest single in-flowing river, the Kagera, which enters the lake from the west.^[10] The only river flowing out of the lake is the White Nile.

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 40 metres (130 ft) compared with a shallowest occurrence of greater than 50 metres (160 ft) in 1961. The changes in oxygenation are considered consistent with measurements of higher algal biomass and productivity.^[11] These changes have arisen for multiple reasons: successive burning within its basin,^[12] soot and ash from which has been deposited over the lake's wide area; from increased nutrient inflows via rivers,^[13] and from increased pollution associated with settlement along its shores.

The lake's eutrophication has also been blamed on the extinction of the cichlid Haplochromis. 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, it is thought that most of Lake Victoria's nutrients are locked up in lake-bottom deposits.^[3][14] By itself, this vegetative matter decays slowly. Animal flesh decays considerably faster, however, and therefore the fertility of the lake is dependent on the rate at which these nutrients can be taken up by fish and other organisms.^[14] There is little doubt that Haplochromis played an important role in returning detritus and plankton back into solution.^[15][16][17] With some 80% 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 and humans.^[15] The removal of Haplochromis, however, may have contributed to the increasing frequency of algal blooms,^[13][16][17] which may in turn be responsible for mass fish kills.^[13]

Before 1954, Lake Victoria's ecology was characterised by enormous biodiversity. It was inhabited by over 500 species of fish, 90% of which were cichlids belonging to the genus Haplochromis.^[18] They are thought to have evolved in Lake Victoria within the last 12,000 years.^[19] They are known for their extraordinary ability to evolve rapidly to suit extremely localised and diverse environments, a characteristic termed 'evolutionary plasticity'.^[17][20][21] This ability has made the cichlid species of Lake Victoria an extremely successful fish. Haplochromis species accounted for some 80% of the fish biomass of the lake,^[18] an abundance which led Graham to believe that this species flock could support a trawler fishery of up to 200 boats.^[22] It also meant that Lake Victoria at one time boasted one of the most diverse fish environments on earth.^[23] With such diversity, the cichlids of Lake Victoria managed to exploit virtually every food source available, including most detritus, zooplankton and phytoplankton.^[17]

Haplochromis species are small and bony, and were generally not favoured in catches. Riparian populations preferred the lake's two endemic species of tilapia (Oreochromis esculentus and O. variabilis).^{[Note 1]} Hence, by the late 1940s, British colonial authorities were debating the overall ecological efficiency of the lake. For many authorities at this time, the lake needed a large and efficient predator to turn Haplochromis fish stocks into something more economically valuable. The prime candidate was the Nile perch (Lates niloticus). Arguments in favour of introducing a predator was as follows:

1. Evidence from other African lakes suggested that the Nile perch could do well commercially, and if the fish were introduced into Lake Victoria, it would no doubt eat the Haplochromis, and hence improve the overall value of the fishery. In addition, it was suggested that by introducing such a fish, fishers might turn their attentions to catching it, so easing some of the pressure on tilapia stocks.^[25] Because the Nile perch can weigh as much as 200 kilograms (440 lb), it was argued, fishers would be encouraged to use large mesh-sizes to capture it.^[25] Furthermore, the perch was said to prefer off-shore habitats, and this would serve to relieve pressure on the in-shore tilapia fishery.^[25][26]
2. In those lakes where the Nile perch was a native it co-existed with tilapia species, and therefore it posed no great danger to commercially important tilapia stocks in Lake Victoria.^[25][26]
3. The potential size of the perch made it a fine sports fish, and this might attract sports fishers and tourists to the lake region.^[26]
4. Finally, archaeological findings close to Lake Victoria suggested that an ancestor of the Nile perch had been native to the Miocene predecessor of Lake Victoria, Lake Karunga.^[27] It was reasoned, then, that if the perch had once been native to the lake, there was little reason why it could not be a native again.^[26][28]

The arguments against its introduction were as follows:

1. Predators can never be as abundant as non-predators because of their nutritional requirements. In other words, the amount of fish a Nile perch has to eat to produce a kilogram of flesh is far greater than the amount of vegetative matter a tilapia has to eat to produce an equal amount of flesh. In ecological terms, the Nile perch is inefficient.^[29] As mentioned above, the fertility of tropical waters depends on the rate at which nutrients (mainly detritus) are brought back into solution. The Nile perch, however, does not eat this detritus, and it was argued that its introduction would do little to improve the over-all ecological efficiency of the lake. If any fish should be introduced, it should be a herbivore or a detrivore.^[3][14]
2. It would be wishful thinking to suppose that the Nile perch would exclusively consume haplochromines.^[29]
3. Given the complexity of tropical ecosystems, it is impossible to predict what might happen should the Nile perch be introduced.^[29]

While the argument continued, it was agreed that tilapia stocks needed bolstering largely as a result of increasing fishing pressure on indigenous species, associated with the expansion of the market for fresh fish in the 1940s.^[5] Tilapia introductions started in the early 1950s with Oreochromis leucostictus from Entebbe, and followed by Tilapia zillii (Winam Gulf, 1953), T. rendalli (Winam Gulf 1953/54), O. niloticus (Kagera River 1954) and O. mossambicus (Entebbe 1961/62).^{[3][23][30][31]} Because tilapia are detrivores and herbivores, these introductions were regarded as less threatening than the introduction of any carnivore. Nevertheless, while the argument over the introduction of the Nile perch raged throughout the early 1960s, it seems that it had already been surreptitiously introduced in 1954 from Uganda.^[20] Once it had been discovered to be in the lake, further official introductions occurred in 1962 and 1963.^[32]

Introduced tilapia species were unable to establish themselves in the lake between the 1950s and 1963. Following unusually heavy rainfall in the early 1960s, however (the so-called 'Uhuru Rains'), the lake-level rose considerably, flooding large areas of shore-line, and opening up new breeding areas to fledgling tilapia stocks, so creating the opportunities for these exotic species to compete with indigenous stocks.^[5] Of the six exotic species introduced, two – Oreochromis niloticus and O. zillii – were to firmly establish themselves in the lake, so that by the early 1980s, these two species comprised the mainstay of tilapia catches. Of the indigenous species, O. esculentus was extirpated from the lake as a consequence of competition with introduced tilapiids, while O. variabilis populations declined significantly.^[31]

The Nile perch is a substantial predator. One specimen, preserved at the Kisumu Museum in Kenya, weighed 184 kg (406 lb) when landed. Populations of the fish established themselves in a clockwise motion around the lake, starting in Uganda, followed by Kenya and ending in Tanzania.^[18] Initial catches were minimal, but grew rapidly in the 1980s, heralding the start of the so-called 'Nile perch boom'. "On the face of it...the lake after the debut of Lates [Nile perch] has turned into a fish producer that can only be described in Gargantuan terms".^[33]

The introduction of the Nile perch had a decisive impact on Haplochromis stocks which it favoured as its prey, affecting both their abundance and diversity. It is believed that the contribution of this species flock to the fish biomass of the lake has decreased from 80% to less than 1% since the introduction of the Nile perch,^[18][34] and that some 65% of the Haplochromis species were driven to extinction in the process, an event which may well represent the largest extinction event amongst vertebrates in the 20th century.^[17]

Freed from their evolutionary predators, populations of the diminutive endemic silver cyprinid Rastrineobola argentea (omena in Luo, mukene in Ganda and dagaa in Swahili), flourished, developing into huge shoals. In turn, Pied Kingfisher (Ceryle rudis) populations, that had hitherto fed on haplochromines, exploded in response to this new food source.^[35] Similar and other impacts have propagated throughout the ecosystem.

Given its 'evolutionary plasticity', it follows that Haplochromis should adapt rapidly to the new environmental conditions generated by the Nile perch 'boom' and eutrophic conditions. Evidence from studies on the lake does suggest that this is happening.^[36] One haplochromine, H. (Yssichromis) pyrrhocephalus, a zooplanktivore, was almost driven to extinction by the Nile perch. This species has recovered alongside increased exploitation of the Nile perch, at a time (the 1990s) when water clarity and dissolved oxygen levels had declined as a consequence of eutrophication.^[37] Over a period of just two decades, H. pyrrhocephalus responded to raised hypoxia (oxygen deficiency) by increasing its gill surface area by 64%. Head length, eye length, and head volume decreased in size, whereas cheek depth increased. The former morphological changes may have occurred to accommodate this increased gill size. Other morphological changes suggest adaptations in response to the availability of larger and tougher prey types.

By the end of the 1940s, fish stocks were under severe pressure. The market for fish grew since railways were available to carry fish to the coast and settlements in between. Improved fishing boats and nets were introduced.^{[Note 2]} British colonial authorities set out to remedy this through the introduction of exotic species, including tilapia and the Nile perch. These introductions had five main impacts. The first of these was the rise of the Nile perch. The fish took some time to establish itself, and only began to appear catch statistics in the mid-1970s. By the 1980s, the 'explosion' of this species was being referred to as the Nile perch 'boom'. Catches climbed from about 335 mt in 1975, to a peak of 380,776 mt in 1990.^{[Note 3]} The second impact was the Nile perch's devastation of the Haplochromis species flock, its main food source. Catches of this species crashed. The third impact related to the lake's diminutive endemic silver cyprinid, the dagaa. Freed from competition (with Haplochromis species) for food sources, this species thrived. It was not the main target of the Nile perch, and catches increased spectacularly from 13,000 mt in 1975, to an all time high 567,268 mt in 2006. The fourth main impact of the introductions related to the exotic tilapia species. One of these, the Nile tilapia (Oreochromis niloticus), was to establish itself firmly in the fishery. Tilapia catches from the lake rose from about 13,000 mt in 1975, to an all time high of around 105,000 mt in 2000. There can be little doubt that these introductions saved the fishery from collapse. With such increases, so too the entire production system on the lake changed, the fifth and final key change. Prior to the arrival of the colonial administration, the fishery was dominated by fishermen (mainly, although certain fishing techniques were reserved for women) who owned their labour and their fishing gear. Contributing to the near-collapse of the fishery in the 1940s and 1950s was the reorganisation of the fishery into fleets drawing on hired labour and much improved gear.^[5][40] The Nile perch 'boom' was to accelerate and massively expand this process. It coincided with an emerging European market for high-quality white fish meat, prompting the development of industrial fish processing capacity along the lake’s shores in Kisumu, Musoma, Mwanza, Entebbe and Jinja.^[41] The export of Nile perch has since expanded away from the European Union (EU) to the Middle East, the United States and Australia, and now represents large foreign exchange earnings to the lake's riparian states. In Uganda, indeed, its export is second only to coffee in the rankings of export earnings. In 2006, the total value of Nile perch exports from the lake was estimated to be US$ 250 million.^[42] The main market for the perch remains the EU, and the industry is, therefore, subject to the worries of EU health and safety inspectors. The EU has frequently closed its doors to the export for reasons ranging from unsatisfactory hygiene at factories to cholera outbreaks on the lake shores.^[38]

With such high demands for Nile perch, the value of the fishery has risen considerably. Labour inflows into the fishery have increased along with growing demand. In 1983, there were an estimated 12,041 boats on the lake. By 2004, there were 51,712, and 153,066 fishermen.^[39] The fishery also generates indirect employment for additional multitudes of fish processors, transporters, factory employees and others. All along the lakeshore, 'boom towns' have developed in response to the demands of fishing crews with money to spend from a day's fishing.^{[Note 4]} These towns resemble shanties, and have little in the way of services. Of the 1,433 landing sites identified in the 2004 frame survey, just 20% had communal lavatory facilities, 4% were served by electricity and 6% were served by a potable water supply.^[39]

The Nile perch fishery has proved controversial, not least between conservationists keen to see the preservation of the lake's unique ecology; and others who recognise the fish's importance to regional economies and poverty alleviation. In the 1990s, one group of thinkers argued that the export of this fish represented a net loss of fish proteins to riparian fishing communities, hence explaining high incidences of malnutrition amongst them.^[44][45][46] 'Empirical evidence ... vividly show that the growing export of the Nile perch and the commercialisation of the dagaa are undermining the survival of households'.^[47] Malnutrition amongst these communities are indeed high; one study estimates that 40.2% of children in fishing communities are stunted.^[48] Rates of childhood malnutrition are, however, lower around the lake than they were in the agricultural hinterland. At fish landing sites, 5.7% of mothers were found to be chronically malnourished.^[48] The latter study, however, argues that these malnutrition levels do not arise from the Nile perch export, but rather as a consequence of gender relations, that tilt income distributions in favour of men, while undermining women's economic status. As the children's primary care givers, this economic status translates directly into the malnutrition rates observed. This economic disparity arises for multiple reasons, including the lack of access that women have to the fishery (very few women actually fish, although some do own fishing boats and gear); children force women to be sedentary (staying close to schools, health facilities and/or social networks), and so are unable to take advantage of the opportunities that emerge through migration, and which are available to men. Women, the authors argue, are forced to exploit peripheral economies, such as the small-scale fish trade, where they must compete against (male) buyers and the fish factories. Women, the study claims, often use sex as a means of developing relationships between fishermen, and so securing a steady supply of fish.^{[Note 5]} While women devote all or most of their income to their children, men have different spending priorities, such as investing in their fishing capacity, drinking and prostitution.^{[Note 6]}

The three countries bordering Lake Victoria – Uganda, Kenya and Tanzania – have agreed in principle to the idea of a tax on Nile perch exports, proceeds to be applied to various measures to benefit local communities and sustain the fishery. However, this tax has not been put into force, enforcement of fisheries and environmental laws generally are lax, and the Nile perch fishery remains in essence a mining operation.

The impact of perch fishing on the local economy is the subject of the documentary Darwin's Nightmare.

There are a number of environmental issues associated with Lake Victoria.

The introduction of exotic fish species such as the Nile perch has altered the freshwater ecosystem of the lake and driven several hundred species of native cichlids to extinction or near extinction.

The water hyacinth Eichhornia crassipes, a native of the tropical Americas, was introduced by Belgian colonists to Rwanda to beautify their holdings and then advanced by natural means to Lake Victoria where it was first sighted in 1988.^[51] There, without any natural enemies, it became an ecological plague, suffocating the lake, diminishing the fish reservoir, and hurting the local economies. By forming thick mats of vegetation it causes difficulties to transportation, fishing, hydroelectric power generation and drinking water supply. The plant also affects water circulation in the lake making it a breeding ground for malaria-carrying mosquitos. By 1995, 90% of the Ugandan coastline was covered by the plant. With mechanical and chemical control of the problem seeming unlikely, the mottled water hyacinth weevil Neochetina eichhorniae was bred and released with good results.

In the late 1990s, the surface area covered by water hyacinth reduced dramatically, for unclear reasons. It is probable that the introduced weevils did serve their purpose, although El Niño weather in 1997/1998 probably also contributed.^[52] It is thought that an improved light climate, an ever increasing supply of nutrients and a potentially unstable weevil population will allow a resurgence of this plant.

Satellite photos from 2006 show that the water hyacinth has re-invaded the lake. The images show that the Kenyan side of the lake around the Gulf of Winam, Kisumu Bay, and Nyakach Bay are covered by the plant. The new proliferation is attributed to the heavy rains that the region experienced in 2006. These rains brought in nutrients that fed the water hyacinth. Ground photos by NASA confirmed the presence of water hyacinth in Kisumu Bay.^[53]

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. Raw sewage decomposes more cleanly in soil, and should be directed back to the ground rather into a drinking water source.

The Lake Victoria basin is one of the most densely populated rural areas in the world. Its shores are dotted with cities and towns, including Kisumu, Kisii, and Homa Bay in Kenya; Kampala, Jinja, and Entebbe in Uganda; and Bukoba, Mwanza and Msoma in Tanzania. These cities and towns also are home to many factories that discharge their waste directly into the lake and its influent rivers. These urban areas also discharge raw sewage into the river increasing its eutrophication that in turn is helping to sustain the invasive water hyacinth.^[53]

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. An excellent map, known as the Al Idrisi map from the calligrapher who developed it and dated from the 1160s, clearly depicts an accurate representation of Lake Victoria, and attributes it as the source of the Nile.

The lake was first 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 on the shores of Lake Tanganyika, was outraged that Speke claimed to have proved his discovery to have been the true source of the Nile, 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 much interest by other explorers keen to either confirm or refute Speke's discovery.^[54]

The famous British 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.^[55] It was ultimately the Welsh-American explorer Henry Morton Stanley, on an expedition funded by the New York Herald newspaper, who confirmed the truth of Speke's discovery, circumnavigating the lake and reporting the great outflow at Ripon Falls on the lake's northern shore.

The only outflow for Lake Victoria is at Jinja, Uganda, where it forms the White Nile. The water 12,000 years ago drained over a natural rock weir. In 1952, British colonial engineers blasted out the weir and reservoir. 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 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,^[56] and was primarily responsible for recent drops in the lake's level.

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 Kenyan independence in 1963 the fastest and most modern ferry, MV Victoria, was designated a Royal Mail Ship. In 1966 train ferry services between Kenya and Tanzania were established with the introduction of MV Uhuru and MV Umoja. The ferry MV Bukoba sank in the lake on May 21, 1996 with a loss of between 800 and 1,000 lives, making it one of Africa's worst maritime disasters.

• Kishanda

• Decreasing levels of Lake Victoria Worry East African Countries
• Bibliography on Water Resources and International Law Peace Palace Library
• New Scientist article on Uganda's violation of the agreed curve for hydroelectric water flow.
• Dams Draining Lake Victoria
• Troubled Waters: The Coming Calamity on Lake Victoria multimedia from CLPMag.org
• Specie List of Lake Victoria Basin Cichlids of Lake Victoria and surrounding lakes
• G. D. Hale Carpenter joined the London School of Hygiene and Tropical Medicine, and took the DM in 1913 with a dissertation on the tsetse fly (Glossina palpalis) and African trypanosomiasis (sleeping sickness). He published: A Naturalist on Lake Victoria, with an Account of Sleeping Sickness and the Tse-tse Fly (1920). T. F. Unwin Ltd, London; Biodiversity Archive

Institutions of the East African Community

• Lake Victoria Development Programme
• Lake Victoria Fisheries Organisation

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