During 2022, extreme rainfall occurred in southeast Australia, making it the wettest year on record in some locations. The impact of extreme rainfall events on the ocean in normally `dry' regions is often not well understood, as their effects on the ocean are challenging to observe. However, extreme rainfall events are known to be important for local fisheries as well as coastal water quality. Using 12 years of data from an ocean mooring and 42 autonomous ocean glider missions maintained as part of the IMOS sustained observing system, we explore the effect of extreme rainfall on the Hawkesbury shelf inshore of the East Australian Current. We find that in 2022 extreme low salinity conditions were widespread and detectable up to 70 km offshore. The compounding effect of multiple large rainfall events resulted in a unique `double-stacked' stratification. This double-stacking was not observed in previous years, or in an idealised modelling study of freshwater inflow. Such events and their associated impacts may become more common as extreme rainfall is projected to become more frequent in a changing climate.