Currently, the problem of environmental pollution, especially in contaminated areas, is highly important. The study of the defense mechanisms of plants under salt stress (high salinity) is of considerable importance, given the conditions of current agricultural development and climate change. The aim of this study was to reveal the effect of salinity on Salix viminalis L. under field conditions at the Stebnyk tailing site in Ukraine. After 120 days of growth, the leaves, stems, and roots of S. viminalis were harvested to measure the antioxidant defense system of plants under salinity. Inhibition of S. viminalis growth was observed. We found that peroxidase, ascorbic acid, and proline mainly accumulated in the stems of S. viminalis under salinity conditions. However, in the roots, an increase in catalase activity and soluble sugars content was observed under salinity stress. Thus, the increase in the amount and changes in the activity of enzymes showed the involvement of the antioxidant system in the adaptation of S. viminalis to salinity. The data obtained in this study serve as a starting point for understanding the adaptive mechanisms of S. viminalis to salinity, particularly at the Stebnyk tailing. We believe our findings will support the use of plants in nature-based solutions and eco-engineering projects on saline and industrially polluted lands.