Major bushfire events are predicted to become more frequent and of greater ‘peak’ magnitude over the next century. In addition to their impact on land-based fauna and flora, bushfires can also affect aquatic systems by increasing the inputs of fire-derived substances and sediment through increased post-fire soil erosion rates and atmospheric deposition of ash. However, there is little scientific information available describing the short- and long-term effects of bushfires on aquatic systems, particularly estuaries. This impedes our ability to take proactive management actions. Aiming to fill this knowledge gap, we conducted the first characterization, to our knowledge, of changes in estuarine sediment quality following major bushfires. We sampled six estuaries in New South Wales, Australia with different fire intensities, areas of catchment burnt, and proximities of bushfire to the estuary. The estuaries were sampled before and after the 2019-2020 bushfire season. We looked at changes in nutrient concentrations (phosphorus (TP) and nitrogen (TN)), different forms of organic carbon (e.g. total carbon (TC), total organic carbon (TOC), resistant organic carbon (ROC), pyrogenic carbon), sediment silt content (<63 um), metals, and chlorophyll concentrations. We recorded an increase in TN, TP, TOC, and silt content in Clyde and Moruya River, the two estuaries that had the greatest percentage of their catchment burnt. In general, we observed consistent changes in the nutrients, carbon, and metal concentrations from pre to post-fire, particularly in the most heavily burnt catchments and in those where the burnt areas extended close to the edge of the waterways, suggesting an increased severity of bushfire impact in these circumstances. These results provide a baseline for the development of environmental indicators of bushfire impact in these systems. We suggest that TOC, ROC, TN, TP, metals, and silt content are useful indicators of bushfire impact and should be incorporated into any long-term study.