The Hau River mouth is the largest estuary of the Mekong River Delta and is strongly influenced by both discharge from the upstream Mekong River and the semi-diurnal tides of the East Sea. This aquatic ecosystem is the interface between upstream freshwater flow and saltwater tidal flow, creating unique aquatic habitats with significant socio-economic importance. The area is densely populated, with many people highly reliant on aquatic ecosystem productivity and related aquaculture cultivation. This study examines changes to water resources in the Hau River mouth based on hydrological variation analysis. There is evidence that, within the last two decades, precipitation is decreasing in the early season but increasing in magnitude towards the end of the wet season. Average water level within the Hau River estuary has increased at about 0.77 cm/year with rising sea level, with concurrent increases in salinity intrusion.  This is resulting in serious water supply limitations and negative impacts on cultivation. Further, the underground water table is declining at a rate of 0.39 m/year, increasing the threat of land subsidence in the region. These factors combine to pose great threats to Mekong River Delta in general and the Hau River mouth area in particular, where water resources face challenges due to climate change and sea level rise, expansion of cultivated areas and water trans-boundary related problems.

Keywords: Hau River mouth, Mekong River Delta; trend analysis; water resources variation.