The supply of nutrients to coastal waters modulates autotrophic production and water quality, yet is often poorly known due to multiple sources, rapid transformations and the limitations of nutrient sampling methods. We present results from the CSIRO 3D hydrodynamic, sediment, optical and biogeochemical model together with continuous nutrient observations from benthic landers, moorings, and gliders to quantify the supply of nutrients to Storm Bay, southeast Tasmania. Seasonal and interannual variability in oceanic nutrient supply is modulated by boundary current extension over the southeast Tasmanian shelf by the East Australia Current in summer and the Zeehan Current in winter. Glider observations show these warm currents of tropical origin to have low nutrient content, however deep nutrient rich water has been observed entering Storm Bay under the East Australia Current and also when these currents are absent from the southern Tasmanian shelf. Elevated nutrient concentrations are also present in river plumes, at localised wastewater and industry discharge outfalls, and at fish farm sites. Observations and modelling shows strong seasonal and interannual variability in Storm Bay water masses, nutrient supply and algal blooms. Scenario simulations quantify the recent and potential future contribution of salmon aquaculture to the system wide nutrient budget.