Salinization of urban streams in temperate climates is a major concern due to increasing salt inputs from sources including road salt de-icers, industrial waste, and landfill leachate. The importance of groundwater pathways in delivering Cl to streams is not well understood. These pathways are important because they represent a year-round persistent input of Cl to streams and also represent a major legacy Cl store in urban areas. This presentation will discuss investigations conducted in multiple urban streams in London, ON, to characterize Cl groundwater inputs to the streams and explore potential impacts. Field investigations include i) large scale longitudinal stream surveys using radon-222 to characterize groundwater Cl inputs along the streams, and ii) high-resolution measurements across a highly Cl impacted stream reach to explore Cl exposure to benthic communities due to groundwater discharge. Novel time-lapse geophysical techniques that are a non-intrusive and efficient approach for mapping Cl contamination in shallow urban groundwater and characterizing the groundwater pathways delivering Cl to urban streams will also be presented.