The block east of the East African Rift tilted eastward. Prior to tilting the rivers probably joined the Congo and flowed west to the Atlantic. One watershed was tilted so far that the course of the river was cut off and the river filled its valleys. The lake now drains out through a former tributary valley and carries the upper Nile. Different colors denote different watersheds.
Boundaries are in red and the horizontal black line is the equator.
See the map below for a detailed view. A detailed map of Lake Kioga. Lakes are in blue and marshes in green. The Nile is in purple with red arrows showing flow directions. To the west is a steep and short drop to the Russian River, but the former valley there was dammed about a million years ago by lava flows.