With the emergence of a Turkish Republic and the mandate territories of Iraq and Syria after the First World War, national and imperial administrations in these new states began planning a series of projects on the Euphrates and Tigris rivers. These plans included new dams, bridges, irrigation and flood control works. The schemes submitted for the two rivers illustrate the aims of development ideologies during the inter-war period as well as understandings of what constituted a modern state. Many of these envisioned water projects were eventually constructed after the Second World War, dramatically altering the flow of the two rivers and remaking the environment of the basin. My research argues that water projects on the two rivers also shaped the environment of state and society by facilitating the rise of a modern bureaucracy, centralizing control over natural resources, justifying new techniques to manage populations, and opening avenues for international intervention. Moreover, the consequences of these changes were not always what governments in Baghdad, Ankara and Damascus intended, producing for local inhabitants a fractured and in many cases discriminative experience of technological advancement and economic “development.” Drawing from an array of primary sources, including government sources, memoirs, and local and national periodicals, this paper explores the planning and implementation of projects in each of the three states. I focus in particular on French plans for a large dam on the Syrian stretch of the Euphrates, the Samarra and al-Ramadi works north of Baghdad, and the Keban dam and hydroelectric station in Turkey. By examining these projects in combination, I expose the political ideas and processes involved in shaping the entire river basin, revealing a story of state formation that is regional rather than bounded by national frontiers.