The Romanian authorities regarded the Danube’s wetlands with suspicion, the health authorities especially turning critical eyes on wet or moist places as constant sources of infectious disease; but many others complained that their economic potential remained untapped. A policy of turning areas of wetland into farmland became therefore an important state-building measure that was aimed at improving both the country’s food security and the health of its population. State actors commissioned specialists to design drainage and cultivation schemes and, after training abroad, young scientists flocked to the Danube to experiment with the scientific methods they had learned. This article examines how the Danube’s floodplain then became a battleground for the conflicting agendas pursued by landowners and leaseholders on the one hand, and government officials and scientists on the other. The most contentious matter turned out to be the question of which particular wetlands should be drained for cultivation and which should be improved to increase fish yield, pitching an alliance of those favouring land extension schemes against those keener to protect fishing grounds. The disagreement split scientific communities and state institutions, but with his vision of a “sustainable” economic exploitation, in the 1930s the biologist Grigore Antipa managed to forge a consensus to harmonize arable and fish farming while setting clear environmental boundaries to human interventions in the floodplain. In practice however, the complex environmental reality and diverging economic interests between state institutions and property administrators meant that many of Antipa’s principles proved difficult to follow.