High de-icing salt applications in cold climates are driving rising chloride (Cl) concentrations in urban groundwater and surface waters, posing risks to water supplies and aquatic ecosystems. Although groundwater discharge is known to influence urban stream salinization, its contribution to lake salinization along urban shorelines remains unclear. This study assessed the utility of geophysical techniques for characterizing groundwater salt plumes along the highly urbanized northern Lake Ontario shoreline, Canada. Electromagnetic induction (EMI) surveys were conducted along 27 shoreline areas to identify locations with potentially elevated groundwater salinity. Two suspected hotspots, Sunnyside and Bluffer’s Park, were then investigated in detail using 3D electrical resistivity tomography (ERT), shallow (<2 m) groundwater and sediment sampling, and horizontal hydraulic gradient measurements. 3D ERT surveys revealed high groundwater salinity at Sunnyside, with Cl concentrations up to 2310 mg/L, while Bluffer’s Park showed lower Cl levels (up to 553 mg/L) but still contained groundwater salt plumes. Hydraulic gradient measurements suggest higher groundwater discharge at Bluffer’s Park, suggesting that Cl loads to the lake may be higher there despite lower concentrations. Overall, this study highlights the potential contribution of lacustrine groundwater discharge to lake salinization and demonstrates the value of rapid, non-invasive geophysical techniques for identifying and characterizing salt plumes along urban shorelines.