Understanding the persistence and extent of freshwater plumes from NSW estuaries—and their impacts on coastal water quality—remains a critical gap in marine estate management. While satellite imagery can map ocean water quality, it faces nearshore challenges due to complex interactions among suspended solids, organic matter, and chlorophyll.
From 2022 to 2025, we assessed optical properties and water quality parameters—including total suspended solids (TSS), coloured dissolved organic matter (CDOM), and dissolved organic carbon—at approximately 180 sites across nine of NSW’s largest estuaries. These in situ measurements enabled the development of new algorithms and a deep learning model, subsequently applied to ten years (2013–2023) of Landsat imagery via CSIRO’s Earth Analytics Science and Innovation (EASI) platform. Our analysis shows optical derived water quality properties varied most along the river-to-ocean gradient, followed by estuarine and seasonal differences.
Using time-series analyses, we produced water quality climatologies, identifying regional patterns and potential hotspots. Combining these outputs with catchment flow data allowed comparisons of TSS and CDOM flux across systems, highlighting which catchments export the largest loads to the open coast. By pinpointing the distribution, severity, and persistence of freshwater plumes, this integrated approach supports targeted interventions and improved coastal water quality across NSW’s marine estate.