Radioecological monitoring of natural waters in the regions of increased probability of radioactive contamination in the territories of the Sverdlovsk and Chelyabinsk regions was carried out. The content of Cs-137 in 27 samples of natural water taken from ponds of Ekaterinburg (Central City, Verkh-Isetsky and Nizhne-Isetsky ponds), lakes - Shartash, Sungul, Bolshiye Kasli, Beloyarsky and Volchikhinsky reservoirs, rivers - Techa, Iset, Rezh, Ivdel, Kakva was studied. Seasonal monitoring of specific activity of Cs-137 was carried out in the most polluted water bodies. It was shown that the content of Cs-137 in surface waters does not exceed the intervention level for drinking water (11 Bq/L). The highest Cs-137 content of 0.61 Bq/L was determined in the waters of the Nizhne-Isetsky pond in November 2021. The lowest content < 0.006 Bq/L - in the Rezh River and Nizhne-Isetsky pond in the summer period. The detected Cs-137 contamination of Nizhne-Isetsky pond waters is presumably related to the Chernobyl trace. The developed method of Cs-137 determination in natural waters was tested. The influence of macro-components of natural waters on caesium yield in concentrate was investigated. It was shown that the method can be used for determination of Cs-137 in waters of any composition and hardness. The yield of Cs-137 in the sorbent concentrate at its determination in natural water samples was 98±2%.