In a semi-arid region, such as southeast Australia, groundwater is the most valuable longterm water resource. A significant part of rural southeast Australia depends on groundwater from the Murray Basin for agricultural, industrial, and, increasingly, domestic water supply. This demand will increase as population grows, and ongoing development of this region relies on the long-term sustainable use of groundwater. Land clearing over the last 200 years following European settlement has resulted in increased recharge leading to land salinisation and waterlogging, degradation of wetlands and rivers, and soil erosion (e.g. Allison et al., 1990; Ghassemi et al., 1995). This has already degraded groundwater and surface water in this region, threatening water supplies, ecosystems, agricultural productivity, and the cultural value of land. Sustainable use of groundwater requires a thorough knowledge of basin hydrogeology, including groundwater flow patterns, origins of solutes, and groundwatersurface water interactions both under present day and pre-land clearing conditions. This paper uses hydrochemistry to describe long-term regional groundwater flow paths and major hydrological processes in the southern Riverine Province of the Murray Basin, Australia.