While many studies have demonstrated the role of stormwater runoff as a primary degrader of streams, none to date have demonstrated an improvement in an urban stream that is the result of mitigation of stormwater impacts. The catchment of a typically degraded urban stream, Little Stringybark Creek, in Melbourne, Australia, was retrofitted to reduce the impacts of stormwater runoff, by treating its quality, retaining it in the urban landscape through infiltration and evapotranspiration, as well as harvesting it as an alternative water resource. Hydrologic and water quality monitoring was undertaken in the study stream along with reference (without urban stormwater impacts) and control (with unmitigated urban stormwater impacts) streams. Runoff coefficients for individual storm events show small but significant reductions over time. Concentrations of suspended sediment, phosphorus and nitrogen reduced substantially following catchment intervention, but salinity levels remained unchanged. Water quality improvements may in part result from reduced sediment transport and increased aquatic macrophyte growth, suggesting that the stream may now, with less frequent disturbance, have greater instream processing capacity. The results are encouraging for stream improvement efforts, but most importantly demonstrate that streams of yet-to-be urbanised catchments could be protected through catchment-wide implementation of stormwater control measures.