The development of the bilateral Long Term Vision for the Scheldt Estuary between 1999 and 2001 reveals that it is possible to move from a history of conflict to cooperation in just two years. A retrospective, insider perspective is used to analyse the integrated three-layer hybrid modelling at the heart of this groundbreaking agreement. We tell an untold story of the collaborative eco-morphological modelling activity that served as a boundary object supporting communication and contributing to a model-based metaphor of the intrinsic character of the estuary – its most lasting contribution.