Coastal wetlands are an important ecosystem in the Great Lakes basin, providing spawning area and warmwater refuge for numerous fish species during cold water upwelling events. Urbanization along the northwestern shore of Lake Ontario has led to a depletion of coastal wetlands, replacing them with artificial embayments. Four artificial embayments, the Credit River Estuary, and one coastal marsh in Mississauga, ON were studied to determine if the artificial embayments function as warmwater refuge during upwelling events. Temperature loggers were placed in each study site and temperature was recorded every 15 minutes from July to October 2017. Upwelling events were isolated from the data, and frequency and extent of upwelling was determined. The results will inform the creation of future embayments, restoration of existing embayments, and conservation of Great Lakes coastal wetlands to create resilient ecosystems.