The ecological turn in water management has usually been interpreted as a political and cultural rather than technical and professional accomplishment. The dynamics of the uptake of ecological expertise into hydraulic engineering bureaucracies have not been well described. Focusing on the controversy around the damming of the Oosterschelde estuary in the Netherlands in the 1970s, this article shows how public environmental politics transformed the politics of interprofessional competition. Andrew Abbott’s concept of “jurisdictional vacancies” is mobilized to illuminate how ecologists took (...) advantage of the political bankruptcy of the Dutch coastal engineering agency to extend their professional jurisdiction. The subsequent “ecologization” of Dutch coastal engineering was successful, however, only because the ecologists were able and willing to adapt their practices to the professional culture of the hegemonic civil engineers. (shrink)