Egypt calls it an “existential threat”. As of next month, Ethiopia says it will begin to fill Africa’s largest pond. How fast? Too fast, for Cairo and Khartoum, both dependent on the Nile. Can the dispute over the Great Ethiopian Renaissance Dam (GERD) be resolved peacefully or can it spiral out of control? Could Egypt’s Abdel Fattah al-Sisi and Ethiopia’s Abiy Ahmed be tempted to gather around the flag when tested at home?