Interactions between groundwater and surface water (GW-SW) strongly influence streamflow dynamics and solute transport, especially in urban catchments where discharging groundwater can be a notable source of contaminants, such as chloride (Cl-). Across the Great Lakes Basin, extensive road salt use has led to chronically high Cl- concentrations in groundwater, raising concerns about its long-term contribution to surface water salinization. Understanding the spatiotemporal dynamics of GW-SW exchange is essential for evaluating Cl- transport and its impacts on urban water quality. This study examines GW-SW interactions and Cl- dynamics in an urban stream in southern Ontario, Canada, over a 2-year field campaign (May 2022 – April 2024), aiming to characterize exchange variability, assess groundwater’s role in shaping in-stream Cl- concentrations, and evaluate local hydrogeologic controls. A multi-method approach was used, including streambed temperature mapping and vertical profiles, seepage meters, hydraulic gradient measurements, and geochemical sampling (δ18O, δ2H, and Cl-) to assess exchange dynamics and relative groundwater contributions. Results revealed spatial variability in groundwater discharge, with persistent upward flow confirmed by temperature-based methods and Darcy’s Law. Concentrations of Cl- in groundwater consistently exceeded aquatic life guidelines (120–640 mg/L), particularly in the streambed drive-points, indicating persistent Cl- loading to surface water, even outside of winter months. These findings highlight the importance of groundwater as a long-term Cl- source in urban streams and demonstrate the value of an integrated approach for evaluating GW-SW interactions in cold-region watersheds.