Which African lake is shared by three countries and holds the most fish species?

Lake Malawi, shared by Malawi, Mozambique and Tanzania, and it contains more fish species than any other lake on Earth - estimates run from 700 to over 1,000, the great majority of them cichlids and the great majority found nowhere else.

That diversity is a textbook case of what evolution does with an isolated body of water and a lot of time. The cichlids have radiated into specialists that scrape algae from rocks, crush snails, eat the scales off other fish, or bite the eyes out of them - and some are confined to a single stretch of shoreline a few kilometres long, so they are separate species divided by a sandy gap they will not cross.

It is also a lake in trouble in ways that are hard to legislate for. Overfishing has collapsed several commercial species, sediment from deforested slopes is smothering the rocky habitats the specialists need, and the aquarium trade takes large numbers of the most colourful. The three countries do not agree on the border either - Malawi claims the whole northern lake to the Tanzanian shore under a colonial-era treaty, which has been a live dispute since oil exploration began.