What is the largest lake in Africa?

Lake Victoria, at about 69,000 square kilometres - the largest tropical lake in the world and second largest freshwater lake by area anywhere. It is shallow for its size, around 40 metres at the deepest, which makes it unusually sensitive to changes in rainfall and evaporation.

It is also young. The lake has dried out completely at least three times, most recently around 15,000 years ago, which makes what happened next remarkable: it holds hundreds of species of cichlid fish found nowhere else, which appear to have evolved from a handful of ancestors in that time. It is the fastest vertebrate radiation known and a standard textbook case of how quickly speciation can happen.

That experiment was then partly destroyed. Nile perch were introduced in the 1950s to improve fishing - they grow to two metres - and hundreds of cichlid species were eaten to extinction or near it. The perch supported a large export industry, and the fish had to be smoked rather than sun-dried because they are oily, which consumed firewood, which cleared shoreline forest. It is the standard case study for introducing a species with the best intentions and no way to undo it.