This study aimed to identify the levels and variability of an array of pollutants in urban stormwater systems that drain into Melbourne’s Yarra River.Pollutant levels varied between catchments, temporally within catchments and temporally during wet-weather events.• The variability of pollutants was found to have a large influence on the accuracy of certain sampling strategies for load estimates.• Comparisons between estimated yearly dry and wet-weather loads showed that for the residential catchment, the total annual load was mainly sourced from wet-weather events. For the industrial catchment, generally less than half of the total annual pollutant load was sourced from wet-weather events.• Results clearly demonstrate that anthropogenic sources of water existed in the industrial catchment and that these sources of water can result in high dry-weather pollutant loads.