Hydraulic improvement aimed to abolish recurrent flooding in wetland commons and generate an environment capable of supporting intensive cultivation. In practice, however, the interventions of Dutch engineer Cornelius Vermuyden and his collaborators created new flooding in unfamiliar patterns and places. As communities were left more exposed to risk and less able to adapt or recover, a fraught hydro-politics rippled out of drainage in Hatfield Level, pivoting on disputes over risk and responsibility. Displacing customary methods of water management, improved hydraulic systems generated institutional as well as environmental disruption. In 1635, a new sewer commission was established to manage Hatfield Level as a hydrological unit defined by improvement. Lacking legitimacy, it struggled to control flow, contain disorderly commoners, or compel cooperation from improving landowners. Wetland communities negotiated new risks by adapting customary practices, launching petitioning campaigns, and high-profile destruction of improved infrastructure during the English civil wars. In this context, water management became highly politicised and precariously balanced.