Аннотация:The urgency of the study is determined by the need to study the radioactive elements migration in different speciations due to their ability to transport beyond the contamination areas and to affect the radioecological situation in the region. The aim of the study is to investigate distribution of 90Sr speciation in the laboratory experiments and directly in the water bodies of the Semipalatinsk Test Site. The methods used in the study: distribution of speciations of 90Sr was studied using sequential cascade fractionation. Total dissolved solids (TDS) and pH were determined by potentiometry using device Anion-4100, and 90Sr content was determined using the method of liquid scintillation counting spectrometry. The results: it has been established that radioactive strontium exists predominantly in dissolved aqueous forms (less than 3 nm). In natural water bodies, which have enhanced concentrations of organic substances, much higher shares of colloidal forms of this radioactive element were observed.