Abstract: The principle of no significant harm has become a cornerstone of international environmental and specifically international water law. Its implementation does, however, regularly lead to disagreements and conflicts between riparian states to shared watercourses as interpretations as to what constitutes significant transboundary harm and whether a certain water resources infrastructure project can move ahead in spite of proven, potential or perceived impacts vary considerably among different states. Some of these conflicts have had severe repercussions on riparian states’ relations and cooperation and stability in the respective region.