To understand transboundary groundwater governance in the South American Guarani Aquifer System, we surveyed global and regional experts about the region&rsquos groundwater quantity and quality, ownership and rights, and regulation and administration. Respondents (1) perceived groundwater quality and withdrawal as under-regulated, and relevant information and data as inadequate (2) suggested that contamination and overdrafting remain mostly incipient and localized along international borders and (3) viewed groundwater as a shared resource administered by the state for the public, rather than as private property. Respondents suggested that while there is progress towards implementing a formal transboundary aquifer agreement, local-to-national-scale governance is important.
