This paper examines the ways in which environmental threats are socially constructed and the implications of such environmental securitisation. Specifically, the paper focuses on the issue of river development and water allocation between states of international transboundary river basins. Building on recent studies that attempt to refine securitisation theory of the Copenhagen School and applying hydropolitical power analysis, the paper takes a sociological understanding of the securitisation of shared waters. Using the case study of the Tanakpur Barrage project on the Mahakali River between Nepal and India in the Ganges River basin, it shows how securitisation discourse framed the shared river as a threat that posed detrimental flooding to both territories. It is argued that the Indian government effectively used its technical and institutional expertise to frame the discourse. Hydropolitical power analysis helps explain how compliance to the project agreement – a necessary measure to avert hydrological crisis, as argued by the Indian government – was gained from the Nepali government. The implications of securitising shared rivers on water resources management and basin-wide governance are discussed.