As the source of 96% of Egypt’s water, the Nile is fundamental to life in Egypt. The division of Nile waters between the states of the Nile Basin has long been a matter of debate and contestation. More recently, Ethiopia’s initiation of a project to build a major dam across the Blue Nile has reignited concerns within Egypt about how upstream withdrawals could affect the country’s water supply. This paper focuses, however, on another factor that will shape the future of the Nile – climate change. As the concentration of greenhouse gases in the atmosphere increases, changing patterns of precipitation in the Nile’s East African source regions have the potential to alter river flows, with profound implications for Egypt. This paper looks at the scientific project to understand the future of the Nile River under climate change. Drawing on interviews with Egyptian and international scientists and participant observation at international water meetings, I examine the process of climatic and hydrological modeling through which scientists probe the future of this critical resource. Due to the difficulty of modeling precipitation dynamics, the range of predictions for Nile flows under climate change remains wide. Indeed this range spans from the positive – a prediction that Nile flows will increase – to the negative – a prediction that they will decrease. I show, first, how different scientists’ responses to this uncertainty are shaped by the position they hold within sociocultural and geographical networks of expertise. Second, I discuss the political ramifications of knowledge about Nile River futures, and how this plays into the way in which different actors present model results – the projections they highlight and those which they underemphasize. Through this analysis, the paper explores how the scientific work of projection shifts and redefines borders. These borders are both temporal – between the present and the future – and spatial – between Egypt and its upstream neighbors in the Nile Basin, between local farmers and the nation, and between scientists working in Egyptian research centers and those working overseas.