Salinisation of floodplains along the Murray River is a significant environmental and social problem in south-eastern Australia that can be expensive and time-consuming to monitor. The potential of plant biogeochemistry as an environmental monitoring tool, specifically its innovative application to groundwater salinity detection, is explored in this paper. Major and trace element biogeochemical data were compared to data from three geophysical surveys in the study area as well as field observations of the underlying stratigraphy. The result is an understanding of how groundwater chemistry can be characterised by plants, specifically river red gum (Eucalyptus camaldulensis) and black box (Eucalyptus largiflorens) leaves. From the survey it is evident that E. camaldulensis and E. largiflorens were both successful in expressing high salinity levels in the subsurface. Molybdenum was the most suitable pathfinder element for high salinity groundwater. The study has important implications for interpreting biogeochemical mineral exploration results; anomalous element concentrations need to be interpreted in relation to salinity levels.