A company flew a Catalina about 15 years ago, landing on lake Baringo, Lake Naivasha, and Lake Victoria... And I have to assume many of the other lakes up and down the rift... Somebody else tried a Lake 270 (?) a while back, but was a bit underpowered for Naivasha.
Of Course the Olb Imperial Airways used to fly London to Cape town in the Empire Flying Boats, the Shorts Sunderland etc, Using The Nile, Lake Kisumu, Lake Naivasha, etc...
Nothing recent that I am aware off, although a Caravan on floats or the Twin otter on floats would be suitable and fun!