During the 2019-2020 Australian bushfire season, large expanses (~ 47%) of agricultural and forested land in the upper Murray River catchment of south-east Australia were burnt. Storm activity and rainfall following the fires generated increased sediment loads within rivers, resulting in localised fish kills and widespread water quality deterioration. We collected water samples from the headwaters of the Murray River for sediment and contaminant analysis as well as assessed changes in water quality using long-term monitoring data. A robust runoff routing model was used to estimate the effect of fire on sediment loads in the Murray River. Peak turbidity in the Murray River reached values up to 4,200 NTU shown as pitch black water coming down the river. The increase in suspended solids was accompanied by elevated nutrient concentrations during post-bushfire runoff events. The model simulations showed that sediment load could be 5 times higher in the first year after bushfire compared to pre-fire condition. It was estimated that Lake Hume, a large reservoir downstream from fire affected areas, would receive a maximum of 600,000 tonnes of sediment per month, in the period immediately following the bushfire, depending on rainfall. Total zinc, arsenic, chromium, nickel, copper and lead concentrations were above the 99% toxicant default guideline values for freshwater ecosystems. It is also likely that increased nutrient loads within Lake Hume will have ongoing implications for algal dynamics, both within the Lake, and in the Murray River downstream. Information from this study provides a valuable basis for future research direction to support bushfire-related policy development in fire-prone catchments and the mitigation of post fire water quality and aquatic ecosystem impacts. This article is protected by copyright. All rights reserved.
2019-20 Bushfire impacts on sediment and contaminant transport following rainfall in the Upper Murray River catchment.