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Lake Victoria

2007 Schools Wikipedia Selection. Related subjects: African Geography

   Lake Victoria
   Lake Victoria - Lake Victoria, as seen from space

                      Lake Victoria, as seen from space

   Coordinates 2°3′S 33°4′E,
   Lake type Rift Valley Lake
   Primary sources Kagera River
   Primary outflows White Nile River
   Catchment area 184,000 km²
   238,900 km² basin
   Basin countries Tanzania
   Uganda
   Kenya
   Max-length 337 km
   Max-width 240 km
   Surface area 68,800 km²
   Average depth 40 m
   Max-depth 84 m
   Water volume 2,750 km³
   Shore length^1 3,440 km
   Surface elevation 1,133 m
   Islands 3,000
   Ssese Islands, Uganda
   Settlements Bukoba, Tanzania
   Mwanza, Tanzania
   Kisumu, Kenya
   Kampala, Uganda
   Entebbe, Uganda
   ^1 Shore length is an imprecise measure which may not be standardized
   for this article.

   Lake Victoria or Victoria Nyanza (also known as Ukerewe and Nalubaale)
   is one of the Great Lakes of Africa.

   Lake Victoria is 68,800 square kilometres (26,560 mi²) in size, making
   it the continent's largest lake, the largest tropical lake in the
   world, and the second largest fresh water lake in the world in terms of
   surface area. Being relatively shallow for its size, with a maximum
   depth of 84 m (276 ft) and a mean depth of 40 m (131 ft), Lake Victoria
   ranks as the seventh largest freshwater lake by volume, containing
   2,750 cubic kilometres (2.2 million acre-feet) of water. It is the
   source of the longest branch of the Nile River, the White Nile, and has
   a catchment area of 184,000 square kilometres (71,040 mi²). The lake
   lies within an elevated plateau in the western part of Africa's Great
   Rift Valley and is subject to territorial administration by Tanzania,
   Uganda and Kenya. The lake has a shoreline of 3,440 km (2138 miles),
   and has more than 3,000 islands, many of which are inhabited. These
   include the Ssese Islands in Uganda, a large group of islands in the
   northwest of the Lake that are becoming a popular destination for
   tourists.

Geology

   Lake Victoria is relatively young; its current basin formed only
   400,000 years ago, when westward-flowing rivers were dammed by an
   upthrown crustal block. The lake's shallowness, limited river inflow,
   and large surface area relative to its volume make it vulnerable to
   climate changes; cores taken from its bottom show that Lake Victoria
   has dried up completely three times since it formed. These drying
   cycles are probably related to past ice ages, which are times when
   precipitation declined globally. The lake last dried out 17,300 years
   ago, and filled again beginning 14,700 years ago; the fantastic
   adaptive radiation of its native cichlids has taken place in the short
   period of time since then.

Exploration history

   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
   Adrisi map dated from the 1160s, clearly depicts an accurate
   representation of Lake Victoria, and attributes it as being the source
   of the Nile.

   The lake was first sighted by Europeans in 1858 when the British
   explorer John Hanning Speke reached its southern shore whilst 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 the then Queen of the United Kingdom. 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 when
   Burton regarded this 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.

   The well known British explorer and missionary David Livingstone failed
   in his attempt to verify Speke's discovery, instead pushing too far
   west and entering the Congo River system instead. It was ultimately the
   American explorer Henry Morton Stanley who confirmed the truth of
   Speke's discovery, circumnavigating the Lake and reporting the great
   outflow at Rippon Falls on the Lake's northern shore. It was on this
   journey that Stanley was said to have greeted the British explorer with
   the famous words Dr. Livingstone, I presume?, upon discovering the
   Scotsman ill and despondent in his camp on the shores of Lake
   Tanganyika.

Ecology and social impacts

   Lake Victoria plays a vital role in supporting the millions of people
   living around its shores, in one of the most densely populated regions
   on earth.

   The ecosystem of Lake Victoria and its surroundings have been badly
   affected by human influence. In 1954, the Nile perch ( Lates niloticus)
   was first introduced into the lake's ecosystem in an attempt to improve
   fishery yields of in the lake. Introduction efforts intensified during
   the very early 1960's. The species was present in small numbers until
   the early to mid 1980's, when it underwent a massive population
   expansion and came to dominate the fish community and ecology of the
   world's largest tropical lake. Also introduced was Nile tilapia
   (Oreochromis niloticus), now an important food fish for local
   consumption. The Nile perch proved ecologically and socioeconomically
   devastating. Together with pollution born of deforestation and
   overpopulation (of both people and domestic animals), the Nile perch
   has brought about a massive transformation in the lake ecosystem and to
   the disappearance of hundreds of endemic haplochromine cichlid species.
   Many of these are now presumed to be extinct.

   Also vanished from Lake Victoria is one of two native species of
   tilapia (another kind of cichlid fish), known as the ngege, Oreochromis
   esculentus. The ngege is superior in taste and texture to Nile tilapia,
   but it does not grow as fast or as large and produces fewer young.
   Ngege and some representatives of haplochromine diversity survive in
   minute swamp ponds and lakes that dot the Lake Victoria Basin. The
   initial good returns on Nile perch catches, at their peak delivering
   export revenues of several hundred million dollars a year, have
   diminished dramatically due to poor enforcement of fisheries
   regulations. The proceeds from Nile perch sales remain an important
   economic engine in the region, but the resulting wealth is very poorly
   distributed and the overall balance sheet on the Nile perch
   introduction to Lake Victoria is well into the red despite the enormous
   value of the perch landings as an export commodity.

   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. Currently, the Nile perch is being overfished. Populations
   of a few endemic cichlid species have increased again, particularly two
   or three species of zooplankton-eating, herring-like cichlids
   (Yssichromis) that school with an abundant native minnow known locally
   as dagaa (Tanzania), omena (Kenya), or mukene (Uganda). In 1996 The
   World Bank funded a project to restore and sustain the ecology of Lake
   Victoria and its fisheries, called LVEMP (Lake Victoria Environmental
   Management Project).

   Meanwhile, the EU invested another large sum in fisheries
   infrastructure and monitoring. Few of the excellent intentions of these
   projects have been actualized despite massive expenditures, but the
   potential for things to be set aright is still great and through it all
   the ecology of Lake Victoria, in its new incarnation, has proven
   amazingly resilient. One beneficial product of these foreign aid
   programs has been the training of a new generation of east African
   aquatic ecologists, conservation professionals, and fisheries
   scientists. There has also been a renaissance in the fishery research
   institutes of the lake. Unfortunately, few of the new professionals
   find jobs, and fewer still find jobs that allow them to apply what they
   have learned to solving, rather than perpetuating, the deep problems
   that still beset the relationship between people and the lake.

   An annual migration of blue wildebeest and other bovids arrives at Lake
   Victoria to find dry season forage. this is one of the largest bovid
   migrations on the African continent.

   An eco-problem with a happier outcome was the fight against the huge
   increase of water hyacinth (Eichhornia crassipes), a native of the
   tropical Americas, which forms thick mats of plant causing difficulties
   to transportation, fishing, hydroelectic power generation and drinking
   water supply. 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 very good results.

Nalubaale dam

   An Island on the Lake
   Enlarge
   An Island on the Lake

   The only outflow for Lake Victoria is at Jinja, Uganda where it forms
   the Victoria Nile. The water originally drained over a natural rock
   weir. In 1954 British colonial engineers blasted out the weir and
   replaced it with the Owens Falls dam, now renamed the Nalubaale dam,
   turning the entire lake into a giant hydroelectric reservoir. A
   standard for mimicking the old rate of outflow called the "agreed
   curve" was established, setting the maximum flow rate at 300 to 1700
   cubic meters per second (392 - 2224 yd³/sec) depending on the lake's
   water level.

   In 2002 Uganda completed a second hydroelectric complex in the area. By
   2006 the water levels in Lake Victoria had reached an 80-year low, and
   Daniel Kull, a hydrologist with the UN's International Strategy for
   Disaster Reduction in Nairobi, Kenya, calculated that Uganda was
   exceeding the agreed curve by 55% .

   At 3500 cubic meters per second (4578 yd³), more than double the
   maximum agreed curve, it would take a year to drain 110.4 cubic km
   (89,500 acre-feet) from the lake. That is approximately 4% of the
   lake's volume.

Transportation

   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. The
   steamer MV Bukoba sank in the lake on May 21, 1996, killing nearly
   1,000 people in one of Africa's worst maritime disasters.

   Retrieved from " http://en.wikipedia.org/wiki/Lake_Victoria"
   This reference article is mainly selected from the English Wikipedia
   with only minor checks and changes (see www.wikipedia.org for details
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