Lake Victoria or Victoria Nyanza (also known as Ukerewe, Nalubaale, Sango, or Lolwe) is one of the African Great Lakes. The lake was named after the United Kingdom's Queen Victoria, by John Hanning Speke, the first European to see the lake.

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

The lake receives most of its water from direct precipitation. Its largest influent is the Kagera River, the mouth of which lies on the lake's western shore. The only river to leave the lake, the White Nile (known as the "Victoria Nile" as it leaves the lake), leaves at Jinja, Uganda, on the lake’s north shore.

Lake Victoria occupies a shallow depression in the East African Plateau, and has a maximum depth of 84 metres (276 ft) and an average depth of 20 metres (66 ft). Its catchment area covers 184,000 square kilometres (71,040 sq mi). The lake has a shoreline of some 4,828 kilometres (3,000 mi), with islands constituting some 3.7% of this length, and is divided between 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).

Lake Victoria supports Africa's largest inland fishery.

Geology

Lake Victoria has, during its geological history, gone through successive changes ranging from its present shallow depression, through to what may have been a series of much smaller lakes. 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. Geologically, the lake is relatively young - about 400,000 years old - and formed when westward-flowing rivers were dammed by an upthrown crustal block.

This geological history probably contributed to the dramatic Cichlid speciation that characterises its ecology, as well as that of other African Great Lakes, although there are researchers who refute 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.

The lake's shallowness, limited river inflow, and large surface area relative to its volume make it vulnerable to the effects of climate changes.

Hydrology and limnology

Lake Victoria receives almost all (80%) of its water from direct precipitation. Average evaporation on the lake is between 2,000–2,200 millimetres (79–87 in) per annum, almost double the precipitation of riparian areas. 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. 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 1960-61, 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 (<>

Other thinkers on the subject blame the lake's eutrophication on the mass extinction of the Haplochromis species 'flock'. 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. 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 eaten up by fish and other organisms. There is little doubt that Haplochromis played an important role in returning detritus and plankton back into solution. 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. The removal of Haplochromis, however, may have contributed to the increasing frequency of algal blooms, which may in turn be responsible for mass fish kills.

credited to wikipedia