Riparian zones are among the world’s most diverse, dynamic and complex biophysical habitats. Unfortunately, they have been degraded on a large scale as a consequence of catchment-scale hydrological modifications, disturbance and contamination linked to urbanisation. This study examined the effects of increased catchment imperviousness (as a surrogate for the intensity of urbanisation) on riparian soil geochemistry in the Georges River catchment in south-west Sydney. Soil sampling was undertaken in the riparian zone of 10 freshwater streams in non-urban and urban catchments in March to June 2013. Soil samples were analysed for key physical and chemical properties (moisture, bulk density, organic matter, pH, salinity, total phosphorus, potassium and calcium). This research found that increased catchment imperviousness was associated with elevated soil and water minerals and nutrients. Mean soil salinity increased 11 times, from 10.0 µS/cm in non-urban catchments to 111.2 µS/cm in highly urbanised catchments. Urban soils had a higher pH (mean 6.5 compared to 5.0 in non-urban catchments) and higher phosphorus (mean 49 mg/kg in non-urban catchments to 390 mg/kg in urban catchments). One of the most interesting findings in this study was that riparian soil calcium levels in highly urbanised catchments (mean 1184 mg/L) were over 2000 times greater than those in non-urban catchments (mean 0.56 mg/L). Changes in these factors are likely to have implications for weed invasion. The most important management message from this current research and review of similar studies is that future urbanisation, particularly in catchments that are currently undisturbed and naturally vegetated, is likely to contribute to the contamination of riparian soils that may modify riparian vegetation communities. We speculate that the source of the calcium in the urban soils is from urban concrete materials with stormwater infrastructure (pipes and gutters) suspected to be a major contributor.