Death of the NILE?

Researchers probed the depths of Lake Tana, the source of the Blue Nile, and showed that the lake dried up at least once in the last 20,000 years. The researchers found a thick layer of brown peat instead of soft, gray-green lake mud which show that the lake has shrunk sometime in the past. They found gray-brown clays below the peat. They concluded that when the lake dried out completely about 17,000 years ago, the clays formed since the papyrus swamp was a transient phase as the lake refilled.