The impact of climate change on the Nile holds great significance for Egypt, which sources almost all its water from the river. Yet the models used to forecast these impacts produce a range of results, spanning from projections of increased flow to the opposite. Such uncertainty, to varying degrees, is a central feature of debates over climate change impacts around the world, and can be put to a variety of political uses. While all scientists negotiate uncertainty in their everyday practice, I focus here on two particular groups: Egyptian and non-Egyptian scientists who are working on modelling Nile futures. First, I examine Egyptian scientists' underplaying of key data uncertainties and link this to their position within national expert networks as predictors of their nation's water futures. Second, I highlight a material dimension to scientists' ability to know, address, and reduce uncertainty. Finally, I argue that Egyptian scientists' selective interpretation of uncertain model outputs, focusing on results that indicate a declining flow, is part of a political effort to bolster Egypt's claim on Nile waters. By exploring uncertainty as a known entity that scientists -not just in Egypt, but in any political context -actively manage, the paper highlights the linkages between the uncertainty of knowledge about various futures and the material, cultural, and political positions of those who produce that knowledge.