How were environments and politics remade by sovereigns, floods, mapmakers, migrants, rioters, and writers during wetland improvement projects in early modern England? Violent Waters examines flagship ventures which promised to transform unruly fenland fringes into orderly terrain at the heart of national power and productivity. In practice, these projects sparked constitutional controversy, new floods, and huge riots. The first state-led project in Hatfield Level brought local, national, and transnational interests into contact and conflict for almost a century. Elly Robson Dezateux traces the environmental politics that emerged as water and land were constructed and contested, both mentally and materially. These disputes pivoted on urgent questions about risk and justice, which became entangled in civil war conflict and exposed the limits of central authority and technology. Ultimately, improvement was destabilised by a lack of legitimacy and the dynamism of local custom as a method of environmental management and collective action. Wetland communities, as much as improvers and sovereigns, remade the terrain of politics and the future of the fens.