The effect of separate and simultaneous action of zinc surplus (1000 μM) and low temperature (4 °C) on growth parameters, photosynthetic apparatus and water exchange in Brassica juncea L. cv. Nika was studied in laboratory settings. Zinc surplus proved to have a greater effect on plant growth and photosynthetic apparatus activity, while low temperature had a greater effecton water exchange indices. To wit, where zinc was in surplus, its content in aboveground organs increased 12-fold, thereby shoot growth was inhibited, photosynthetic pigment content and water content of leaf tissues decreased, photosynthesis rate slowed down. When exposed to hypothermia but with optimal zinc availability, the plants were able to maintain the required photosynthesis rate, with photosynthetic pigments and leaf tissue water content remaining at the control level or even higher. However, the transpiration rate decreased significantly (compared to optimal growth conditions) and the photosynthetic water use efficiency (WUE) increased. No synergistic effect on growth and photosynthesis parameters was observed under simultaneous exposure to these stress factors: the inhibition of shoot height and shoot weight (compared to optimal growth conditions) as well as the photosynthesis rate was nearly the same as under the action of zinc surplus alone. At the same time, the metal content in plants in this treatment was lower than in the variant with zinc surplus and optimal temperature. The only index affected more severely by the simultaneous action of the two stress factors compared to exposure to each of them separately was the transpiration rate. We conclude that Sarepta mustard is highly resistant to both zinc surplus and low temperature as well as to their simultaneous action, which is due, at least in part, to adaptive changes in the photosynthetic apparatus and water exchange. The results of the study demonstrate the practicality of using Sarepta mustard cv. Nika in phytoremediation of zinc-contaminated areas, including in northern regions.