Sea level rise and upstream development is causing salinity intrusion in Vietnam’s Mekong River Delta (MRD) and, as a consequence, agricultural productivity is declining. As the Vietnamese government and local communities search for a solution, it has become apparent that there are insufficient public resources to build the dykes necessary to control this problem. So, we employ a referendum contingent valuation methodology (CVM) to determine whether or not farm households might be willing to pay for part of the cost of a salinity intrusion risk reduction program. We find that farm households are willing to contribute funds to such a program. In areas where salinity intrusion is already reducing productivity, farm households are willing to contribute US$2.58 per month. In areas where salinity intrusion is expected to be reducing productivity by 2030, willingness to contribute is US$1.99 per month. Surprisingly, in MRD areas where salinity intrusion is not expected within the next 15 years, willingness to contribute remains positive at US$1.32 per month. These findings have local, national and international implications that require careful consideration. In passing, we make a methodological observation that a treatment model including ‘do not know’ responses provides consistent results with conventional referendum elicitation procedures.