Some biological implications of a revised geological history for Lake Victoria

Lake Victoria has long been advanced as an example of a lake in which the physical limnological changes have proceeded side by side with biological changes. The paper summarizes recent geological findings and indicates the necessity of revising assumptions made in the biological literature concerning the geological evolution of the lake. It is argued that the revised geological history provides a simple explanation of the main features of the lake ichthyofauna. It is also consistent with the known biological changes.

A mid-Pleistocene inception is postulated for the lake; it was formed as a shallow basin resulting from cross-warping of a well-developed westward-flowing plateau drainage. In its early stages, as the pre-lake rivers were ponded-up, several separate dendritic, swampy lakes must have existed. These gradually became interconnected, lost their outlet to the west and were drained northwards by the Nile. Subsequent fluctuations in level have been generally negative and have resulted from incision of the lake outflow not climatic change.