The ecological turn in water management has usually been interpreted as a political andcultural rather than technical and professional accomplishment. The dynamics of theuptake of ecological expertise into hydraulic engineering bureaucracies have not beenwell described. Focusing on the controversy around the damming of the Oosterscheldeestuary in the Netherlands in the 1970s, this article shows how public environmental politicstransformed the politics of interprofessional competition. Andrew Abbott's conceptof "jurisdictional vacancies" is mobilized to illuminate how ecologists took advantageof the political bankruptcy of the Dutch coastal engineering agency to extend their professionaljurisdiction. The subsequent "ecologization" of Dutch coastal engineeringwas successful, however, only because the ecologists were able and willing to adapt theirpractices to the professional culture of the hegemonic civil engineers.