The 2019/2020 Black Summer wildfires burnt ~300,000 ha, or ~80% of the designated special areas catchment surrounding Lake Burragorang, impacting almost a third of the total catchment which supplies Warragamba Dam, the source of up to 80% of Sydney’s raw drinking water. Within weeks of the local Green Wattle Creek Fire being contained, a 1 in 39-year rainfall event occurred across the region, resulting in ~800,000 ML of inflows into Lake Burragorang, and a doubling pre-storm lake volume. Post-fire, a range of water quality monitoring was undertaken to understand the water quality changes within the lake. This was augmented by erosion modelling, sediment transport and deposition assessment. Most monitoring focused on using established water quality analysis by WaterNSW routine laboratory providers for known fire related contaminants such as pyrolysis products, metals, nutrients and changes in turbidity, colour and algal response. Specialist analysis was conducted for changes in organic matter composition, radionuclide analyses for sediment tracking and bacterial sequencing to assess likely sources of taste and odour compounds. Pyrolysis products and pathogens were below detection limits at the dam wall. Manganese, true colour, dissolved organic carbon, nitrogen and filtered iron all showed greater fluxes in the fire-related 2020 plume within the lake when compared with historical non-fire related sediment intrusions, while aluminium, total iron, phosphorous and TOC fluxes did not appear to increase with the effect of fire. While water quality was managed with no impacts to drinking water supply, the ability to model and accurately predict contaminant generation and transport to lakes in fire-affected catchments posed a significant challenge. To address this gap a comprehensive research program has been initiated to increase understanding and improve modelling tools for future fire response.