Lake VictoriaFrom Wikipedia, the free encyclopedia

For other places with the same name, see Lake Victoria (disambiguation).

Lake Victoria

Location Africa

Coordinates 1°S 33°ECoordinates: 

1°S 33°E

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 84 (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 (Nam Lolwe in Luo; "Nalubaale" in Luganda; Victoria Nyanza in Bantu [1]  ) is one of

the African Great Lakes. The lake was named after Queen Victoria by the explorer John Hanning Speke,

who was the first European to discover it, and which he did alone in 1858 while on an expedition

with Richard Francis Burton to locate the source of the Nile River.[2] [3]

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 2nd 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 ninth largest continental lake, and it contains about 2,750 cubic kilometers (2.2 billion acre-feet) of

water.

Lake Victoria receives its water primarily from direct precipitation and thousands of small streams. The

largest stream flowing into this lake is theKagera River, the mouth of which lies on the lake's western shore.

Lake Victoria is drained by the Nile River (generally known as the Victoria Nile, part of the White Nile)

near Jinja , Uganda , on the lake's northern shore.[4]

Lake Victoria occupies a shallow depression in Africa and has a maximum depth of 84 m (276 ft) and an

average depth of 40 m (130 ft).[5] Itscatchment area covers 184,000 square kilometers (71,040 sq mi). The

lake has a shoreline of 4,828 km (3,000 mi), with islands constituting 3.7% of this length,[6] and is divided

among three countries: Kenya (6% or 4,100 km2 or 1,600 sq mi), Uganda (45% or 31,000 km2 or

12,000 sq mi) andTanzania (49% or 33,700 km2 or 13,000 sq mi).[7]

Contents

  [hide] 

1 Geology

2 Hydrology and limnology

3 Fisheries

4 Environmental issues

o 4.1 Fishing

o 4.2 Water hyacinth invasion

o 4.3 Pollution

5 History and exploration

6 Nalubaale Dam

7 Transport

8 See also

9 References

10 External links

Geology[edit]

Landsat 7 imagery of Lake Victoria

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.[6] Geological cores taken from

its bottom show Lake Victoria has dried up completely at least three times since it formed.[8] These drying

cycles are probably related to past ice ages, which were times when precipitation declined globally.[8] 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.[8]

Lake Victoria and the Great Rift Valley

This geological history probably contributed to the dramatic cichlid speciation that characterises its ecology,

as well as that of other African Great Lakes,[9] although some researchers dispute this, arguing while Lake

Victoria was at its lowest between 18,000 and 14,000 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.[10]

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.

Hydrology and limnology[edit]

Lake Victoria receives 80% of its water from direct precipitation.[6] Average evaporation on the lake is

between 2.0 and 2.2 metres (6.6 and 7.2 ft) per year, almost double the precipitation of riparian areas.[11] 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

inflowing river, the Kagera, which enters the lake from the west.[12] The lake outflows into the White Nile and

the Katonga River , both part of the upper Nile river system.

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.

[13] These changes have arisen for multiple reasons: successive burning within its basin,[14] soot and ash

from which has been deposited over the lake's wide area; from increased nutrient inflows via rivers,[15] and

from increased pollution associated with settlement along its shores.

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.[6][16] 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.[16] There is

little doubt that Haplochromis played an important role in returning detritus and plankton back into solution.

[17][18][19] 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.[17] The removal of Haplochromis, however, may have contributed to the increasing frequency

of algal blooms,[15][18][19] which may in turn be responsible for mass fish kills.[15]

Fisheries[edit]

Main article: Fishing on Lake Victoria

Lake Victoria supports Africa's largest inland fishery.[20]

Environmental issues[edit]

A number of environmental issues are associated with Lake Victoria.

Fishing[edit]

The introduction of exotic fish species, especially the Nile perch, has altered the freshwater ecosystem of

the lake and driven several hundred species of native cichlids to near or total extinction.

Water hyacinth invasion[edit]

Main article: Water hyacinth in Lake Victoria

The Water hyacinth has become a major invasive plant species in Lake Victoria. The release of large

amounts of untreated wastewater (sewage), 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 1990’s”.[21][22] 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.[21][23]

[24][25][26] On the flip side, 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. However, the overall effects of the Water

hyacinth are still unknown.[23][27]

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.[23] 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).[26] 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.[26] 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.[26][28][29][30]

Other factors which may have contributed to the decline of the Water hyacinth in Lake Victoria include

varying weather patterns, such as El Nino 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 however, simply moved to another location. Additionally, the water

quality and nutrient supply, temperature and other environmental factors could have played a role. Overall

the timing of 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.[26] The Water hyacinth is in remission and

this trend could be permanent if control efforts are continued.[31]

Pollution[edit]

Population density around Lake Victoria

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 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.[32]

History and exploration[edit]

Bismack Rock

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 as it is visible from the shores of the Speke Resort in Kampala, Uganda

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 also much interest by other explorers keen to either confirm or refute

Speke's discovery.[33]

In the past, 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.

[34] 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.

Local languages around lake Victoria

Nalubaale Dam[edit]

Main article: Nalubaale Power Station

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,[35] and was primarily responsible for recent

drops in the lake's level.

Transport[edit]

Main article: Lake Victoria ferries

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.