The Omo river in Ethiopia has been dammed- and damned. Read this to find out more:
http://newswatch.nationalgeographic.com/2010/08/04/omo_river_dam_threatens_traditional_farmers/
Now it is the turn of the Blue Nile with the giant Renaissance dam project. It will destroy and disrupt far more than people imagine. An early 'ecological appraisal' stated only 800 people might lose their livlihoods when the 2000 square km lake is filled. It will be more like 8000. Or maybe more. this lake is about a third the size of lake Nasser- which caused an entire people - the Nubians- to lose their homeland, over 100,000 moved or displaced.