This article assimilates the city of Phnom Penh into an open system that has spread into the Mekong River flood plain with the backfilling of tidelands and the building of successive dykes. The city's hydraulic networks were damaged by the major crisis suffered under the Khmer Rouge characterized by a strong de-urbanization process. Since 1979, the progressive restoration of institutions, in addition to ad hoc interventions in the city's networks by ‘pioneer actors’, allowed vertical interactions in the city-system between stakeholders and structures to redevelop, and also permitted horizontal interactions between structures. Despite more recent crises, the city-system has proved resilient and it maintains its dualistic kernel–margins structure.