This contribution focuses on the discrepancies existing between general frameworks defined at the international level and the need for the implementation of context-specific arrangements to solve water management challenges at the transboundary level. Relying on an institutionalist perspective and on a qualitative methodology, we analyse how international law is implemented, completed and instrumentalized at the transboundary level. We focus on institutional crafting (Ostrom 1992) to grasp harmonisation of uncoordinated legal frameworks. Analysing the process of defining institutions, we ask the following research questions: How international water law is materialized at the local level? How do stakeholders mobilize a legal framework in order to solve collective action problems at the transboundary level? How do institutions evolve and how are they continuously crafted in order to define a tailor-made and context-specific arrangement? We focus on a sediment flushing operated in spring 2012 on the dam of Verbois.