Kafrican, errrmmh.. you erred kidogo pale. Actually its the other way round: River Omo is the primary inflow for lake Turkana. It does not flow into the Blue Nile nor do any of its tributaries. The lake has its own basin which is an "island" basin in relation to its neighbours.
Actually, truth be said, the damming of River Omo was going to be the potential death of L Turkana. The other two inflow rivers(Turkwell and Kerio) are also perennial . Keep in mind the lake has no outflows and being in the desert, maybe 10 % or more is lost to evaporation. They alternate in providing water to the lake, hence why its mostly more than half full.
As the Omo itself has unreliable flow can you imagine what would happen in a drought situation when the need to keep a tankful of water to drive a turbine overrides that of keeping a lake alive? And the Gibe I to III dams are being built for exporting electricity. Especially to its southern neighbour.
The decision by the Ethiopians to build the dam without proper consultation on water rights was an unmitigated disaster on our part by every measure, seeing as we aren't at war. Smacks of arrogance on their part and bungling on ours. All the same its not too late to save the day, they can agree on the watershed management and propose amelioration measures such as water harvesting in the South Ethiopian region where the Omo rises. At least that way, in a drought, groundwater will still feed the river.
By the way, these Ethiopians are not angels and goody goody neighbours, they are very sneaky. Remember how they hijacked the Arab Spring riots and the resulting power vacuum in Egypt to start building the Rennaisance dam??