In the Mekong Delta region of southern Vietnam, salt water has long been considered a threat to development and a constraint to agriculture. Consequently, a line of anti-salinity defenses – from dikes to dams to giant sluice gates – has been built up over time to keep the tides at bay and protect rice-growing farmland from saline intrusion. In recent years, however, these defenses have been challenged both from the outside – by global sea level rise – and from within – by those seeking to switch from rice agriculture to saltwater shrimp aquaculture for international export markets. Over the last decade, dikes have been demolished, irrigation canals re-purposed for shrimp aquaculture, and massive sluice gates opened to allow the unimpeded flow of saline water into once-protected farmland. While much attention has been paid to sea level rise as an external driver of environmental change in the Mekong Delta and in Vietnam more broadly, this research project looks instead at the situated, social, and contested nature of salinization. To do so, I employ a mixed-methods approach – drawing upon geo-spatial analysis, participatory mapping, surveys, ethnographic observation, and key informant interviews – to explore how salinization is produced through society-nature relations, how it simultaneously works through and reshapes access to resources and the distribution of productive assets, and how it is contested politically at multiple scales. By working from within a case study of the Mekong Delta province of Soc Trang, I will argue that the ongoing process of salinization provides a window onto changes in human-nature interactions and technologies of water control, shifting social relations of property, and competing visions of development and resource governance in Vietnam.