The relevance of the study is defined by the ability of technogenic radionuclides contained in significant quantities in surface water bodies of the Semipalatinsk test site, to move beyond the nuclear test sites. This ability is determined by the speciations of radioactive elements. The issue of migration and influence of species of technogenic radionuclides in water bodies has not been studied enough to predict the behavior of radioactive elements on a longterm basis. The aim of the work is to study the speciation of radionuclides in the water bodies of the Semipalatinsk test site. Methods. Distribution of species of radioactive elements was studied using the sequential cascade fractionation. Water pH was defined potentiometrically using Anion-4100 devise. The components of chemical composition of natural water and total dissolved solids were determined in accordance with All Union State standard 26449.1-85. The content of dissolved organic matter was identified by the dichromatic oxidation method with a measurement on a PE-5300VI spectrophotometer. The content of radioactive isotopes was determined by radiochemical separation methods with the preparation of a counting sample for alpha spectrometry of 239-240 Pu, liquid-scintillation beta spectrometry of 90 Sr, and highly sensitive gamma spectrometry with a well type hidh-purity germanium semiconductor detector after preconcentration for 137 Cs and 241 Am. Results. The cascade fractionation method using a set of membranes with decreasing pore size is suitable for separation of suspended, pseudocolloidal, colloidal and dissolved species in natural waters. The author has obtained the data of chemical and isotopic composition of individual water bodies of the Semipalatinsk test site as well as content and speciations of radionuclides. It was found that 137 Cs in water migrates in colloid and dissolved forms, the predominant species of 90 Sr is dissolved, fractionation of 239-240 Pu was specific for each water body. The water of the waterstream outflowing from tunnel No. 177 is characterized by the predominance of dissolved form for all studied radionuclides.