AbstractThe water quality parameters, like major ions, have been monitored at three stations located along the Syr Darya River. The trend analysis was performed on annual timescales using the Mann–Kendall test, the Sen’s slope estimator and the linear regression. The relationships of the water quality parameters to river discharge were also investigated. The statistical methods showed both positive and negative trends in annual water quality data and major ions. Significant trends were detected by the statistical methods in sulphate, sodium-potassium ion and chloride ion series. Before 1940 the mineralization of water was 0.4–0.6 g/L and the water was bicarbonate-calcium, with an increased sulfate ions volume. Atthe moment, the mineralization index has become three times higher. The mineralization varies from 0.9–1.2 g/L in the upper and 1.5–2.0 g/L in the lower reaches of the river. The sulfate ion and sodium-potassium ions began to predominate, dangerously exceeded volumes of the chloride ion in the lower part of the river are observed.