How were England’s wetland margins imagined at a new scale, as a site of reform and profit at the heart of a thriving polity? This chapter traces the iterative rewriting of wetlands in histories, geographies, agricultural books, and pro-drainage pamphlets at the turn of the seventeenth century. Driven by desires to unify England and amplify national wealth, these improving authors reconceived the meanings and management of wetlands and common lands. Scholars have often identified this period as a hinge between long-standing beliefs that topography and climate shaped human bodies and societies and a new conviction that soil, water, and air could and should be altered through human intervention. This chapter suggests that environmental determinism and environmental reform were not antithetical impulses but instead two sides of the same coin. Improving authors interlaced older humoral theories with new ideas about political economy to articulate fen futures. In recasting wetlands as unruly, unhealthy, and unproductive, ambitious wetland projects became a ‘cure’ for the nation’s most pressing maladies, promising to produce productive land and industrious subjects.