Climate change is projected to have catastrophic impacts on the hydrological cycle. Responding to its projected adverse impacts requires building flexibility and adaptability into watercourse treaties. Exploring the treaty practices of other shared watercourses, this Article studies the context of the Nile Basin, and concludes that the legal regime governing the Basin lacks the flexibility needed to adapt to climate change. It argues that the Declaration of Principle, which contemplates a flexible agreement for governing the Grand Ethiopian Renaissance Dam, is a step in the right direction. It also proposes mechanisms for governing the Nile under climatic uncertainty, and calls upon Nile Basin States and other water-sharing States to set aside their egoistic national interests and develop climate-proof treaties.