River regulation and flow modification have severely impacted riverine ecosystems throughout the world, including the Murray–Darling Basin (MDB). The Lower Murray River (LMR) is one of the most highly regulated, with natural flow regimes substantially altered (e.g. decreases in discharge, hydraulic variability, and floodplain inundation). The construction of multiple low-level (<3 m) weirs has changed a connected flowing river to a series of weir pools. These have resulted in profound impacts on riverine processes and ecosystems.
Over more than a decade, environmental flows have been used in the MDB to re-establish key features of the natural flow regime to restore ecosystem health; the LMR represents a key target for environmental watering with ecological monitoring implemented since 2011-12 funded by Commonwealth Environmental Water Office. The indicators included hydraulic regime, salt/matter transport, Coorong habitat, stream metabolism, vegetation, zooplankton and fish. Empirical data collection and modelling was conducted over 11 years (2011–2022) under varying hydrological conditions (dry to flood years) supported with different environmental water deliveries. This helped to evaluate the contribution of environmental water to ecological outcomes and improved our understanding of biological/ecological responses to flow regimes, informing adaptive management. Our work highlights the importance of environmental water, particularly during dry years, in maintaining riverine flowing habitat, connectivity, salt export, Coorong estuarine habitat, and potentially contributing to the recruitment and population maintenance of some fish species. Furthermore, a coordinated and collaborative approach is critical in environmental flow management across the southern MDB to achieve the ecological outcomes in the LMR.