Africa’s largest lake lives mostly on rainfall, not rivers
Lake Victoria covers about 59,947 square kilometres: Africa’s largest lake, the world’s largest tropical lake, and second only to Superior among freshwater surfaces. Tanzania holds forty-nine percent, Uganda forty-five and Kenya just six, and roughly four-fifths of its water falls straight from the sky rather than arriving by river.
John Hanning Speke renamed local Nyanza waters for Queen Victoria after documenting them in 1858. Geologically the basin is young, around 400,000 years, formed when westward rivers were dammed into a shallow depression that has dried completely more than once. Sediment cores show it has vanished entirely at least three times since it formed. For so broad a lake it is shallow, averaging about 40 metres and reaching roughly 80, and only in 2016 did a project digitising ten thousand soundings produce its first true depth map.
About eighty percent of water arrives as direct rain; evaporation of 2.0–2.2 metres per year nearly doubles riparian rainfall. The Kagera and countless streams add the rest. On the Kenyan side the Sio, Nzoia, Yala, Nyando, Sondu Miriu and Migori all flow in, while the single exit is the Nile near Jinja in Uganda, making Victoria the chief source of the river’s longest branch.
More than 500 haplochromine cichlid species evolved here, nearly all endemic, with bright males, drab females and diets spanning at least 16 niches from detritus to other fish. Endemic cichlids once thronged the shallows until invasive Nile perch drove many extinctions. A large share has disappeared since the 1940s. Hippos, two kinds of otter, sitatunga antelope, Nile crocodiles and the Williams’ mud turtle of the upper Nile basin also depend on the lake and its wetlands.
Eutrophic chemistry and shifting oxygen profiles mark modern surveys; between 2010 and 2022 surface area grew about fifteen percent, flooding lakeside communities. Multiple local names—Nam Lolwe, Nnalubaale, Nyanza—still compete with the colonial label.
Source: Lake Victoria
