How well is the basin plan meeting its objectives? From the perspective of the Coorong, a sentinel of change in the Murray-Darling Basin

Freshwater aquatic ecosystems can be considered sentinels of change as they integrate signals from catchment, hydrology and biogeochemistry to provide an indication of how the system fluctuates. The Coorong estuary acts as a sentinel for the Murray-Darling Basin (MDB), Australia. Its location at the terminus of the Murray-Darling River systems, which drains more than 1 million square kilometres across 22 major catchments, means that any change to climate, water extraction or land use in the upstream catchments will have repercussions for the Coorong. It therefore acts as an indicator of the health of the MDB and the effectiveness of the Murray-Darling Basin Plan at protecting this ecosystem. Environmental water secured through the Murray-Darling Basin Plan and establishment of the Commonwealth Environmental Water Holder has been critical to preventing significant ecosystem decline in the Coorong. For most water years in the last decade environmental water has contributed to the majority of flow through the barrages. This has exported salt from the basin, reduced influx of salt from the ocean, and expanded available habitat for fish in the Coorong. However, the environmental flows have not been sufficient to arrest sand build up, and dredges still operate at the Murray Mouth during all but the highest flow events. There is a clear case for continued water management and reform, extending beyond the boundaries of the MDB, to further increase security of water flowing along the river system through the barrages and supporting the ecological health of the Coorong, and by association the full MDB.