Salinization of South African rivers is serious and has rendered some dams and reservoirs unsuitable for irrigation. The contribution of agriculture to the environmental problem of salinization was empirically analysed in this study. Linear regression models demonstrated that increases in the Total Dissolved Salts (TDS) and chlorine of the Olifants River in the Loskop Valley are at least partially the result of variations in irrigation farming parameters such as fertilizer usage, rainfall and area cultivated to crops such as tobacco, cotton and wheat. The marginal rates of substitution among the independent variables can be employed in the formulation of the economically most efficient local salinization control policy. Other approaches are possible, but should be adopted only after thorough investigation.