The researchers developed and tested a model called MOPUS to predict microorganism levels in urban stormwater. The model combines surface and subsurface components to simulate microorganism build-up and wash-off from impervious surfaces and stormwater pipes. By using a simplified approach with few calibration coefficients, the model accurately predicted E. coli levels in stormwater from four urban catchments in Melbourne. The predictions were good for flow rates, E. coli concentrations, peaks, loads, and mean concentrations. Overall, MOPUS shows promise for reliably predicting E. coli discharges in urban stormwater systems, making it a useful tool for planning in urban areas.