Natural hydrologic pathways can act as buffers that attenuate effects of human land use in catchments.  I assessed if modeling attenuation along drainage lines improved predictive models of urban land use on 3 indicators (macroinvertebrate assemblage composition, and median concentrations of Escherichia coli and nitrate/nitrite) in streams of Melbourne, Australia.  For each indicator, 13 models were calculated using imperviousness or septic tank density, or both, as predictors, variously with no attenuation, with overland attenuation (either to the nearest stormwater drain or stream), and with overland and instream attenuation.  The best model for each indicator was determined using the Akaike Information Criterion.  E. coli was best predicted by septic tanks within 10¹ m of streams, and with attenuation over 10³ m along streams, suggesting natural hydrologic pathways attenuate bacterial contamination, and that stormwater sewers are not important pathways for septic leakage in this area.  Nitrate/nitrate, which is mobile through soils, was best predicted by simple septic tank density.  Macroinvertebrates were best predicted by impervious areas within 10¹ m of stormwater drains, suggesting they are most strongly affected by stormwater runoff routed through stormwater pipes to streams.  Stream protection from urban impacts requires management of drainage pathways to maximize their attenuating effects.