The Mekong Delta faces major land and water challenges. Agriculture production in the downstream areas is currently constrained by salinity intrusion in the dry season. Climate change will most likely increase salinity concentration levels in the dry season due to a combination of higher sea level and lower upstream river flows. Adapting to increased salinity may involve changing cropping patterns, constructing new water infrastructure or abandoning land. We analyze the economics of adapting agriculture to increased salinity in the coastal districts of Long An province. Results suggest that productivity losses can be alleviated by shifting to high value and more salt-resistant crops. We also find that the optimal timing for investment in water infrastructure depends on the rate of increase in salinity levels and that there is a tradeoff between protecting upstream areas versus areas that are closer to the sea.