The Rundu – Grootfontein Project, a project by which Namibia wants to divert waters of the Okavango river, may significantly affect the flow of that river through Botswana. The present paper discusses and tests rules of global and regional international watercourse law as to their applicability to the problems posed by the project. In this respect the UN Framework Convention on the Law of the Non-Navigational Uses of International Watercourses, as well as the Southern African Development Community Protocol on Shared Watercourses form the main focal point.