Shallow-constructed ponds are ubiquitous features of the urban landscape; however, their full impact on downstream water quality remains unquantified. While recent research has demonstrated urban ponds experience thermal stratification for prolonged periods in the summer, the duration of inverse thermal stratification during winter months has received less attention. We investigated these dynamics in Mississauga, Ontario by taking water quality parameters at multiple locations in a stormwater management pond (SWMP) and a nearby “control” natural pond without inflows and outflows. We measured electrical conductivity, temperature, dissolved oxygen, and pH at the surface, middle, and bottom depths at four locations in both ponds approximately weekly from October to April. The forebay area nearest the inflow had a greater salinity-driven density stratification compared to other sampling locations. The SWMP was inversely thermally stratified for a longer duration (11 weeks) than the natural pond (1 week). This was likely due to large inputs of de-icing road salt into the SWMP: electrical conductivity near the inlet at depth changed from 2,903 µS/cm on December 12th to 6,271 µS/cm on January 24th while surface conductivity remained below 1,800 µS/cm. Comparatively, surface-depth EC differences in the natural pond during this time were 145.40 µS/cm or less. Despite continual flushing of surface water through the SWMP, salinity-driven stratification during winter can lead to sustained discharge of low-oxygen water (1.34 ± 0.57 mg/L) to the downstream environment. Understanding internal dynamics of SWMPs in wintertime conditions will aid land managers in impact assessment of downstream ecosystems throughout the year.