This paper presents the new water challenges experienced by rural societies in the Vietnamese Mekong Delta (VMD) under the compounding effects of climate change, hydropower development and local water-engineering infrastructures. These are linked to extreme hydrological alterations over the past few years that disturb agrosystems and related means of livelihoods of rural communities in both flooding and salinity areas of the delta. Drawing on interviews and discussions with key stakeholders in the VMD and the study of public and policy documents, the paper argues that, while climate change comparatively receives dominant attention, transboundary implications (upstream hydropower developments) are not fully acknowleged in water governance and adaptation policies at the central and delta levels. The study urges the critical consideration of this policy gap in decision-making processes across governance scales in response to the ‘new normal’ of water challenges facing the delta in the future.