The Semipalatinsk test site, one of the largest and the first nuclear test site on the territory of the USSR used until 1991, remains a large radioactive site with a constant threat. The content of Sr⁹⁰ and Cs¹³⁷ was addressed in freshwater fish caught in the Irtysh River. The purpose of the research was to determine the degree of activity of Cs¹³⁷ and Sr⁹⁰ in Bq/kg, which means the specific activity of the radionuclide‑ratio of the activity of the radionuclide in the radioactive image to the mass of the sample.In the course of the study, a prospective uncontrolled study of radionuclide content (Sr⁹⁰  and Cs¹³⁷) in muscle tissues of freshwater fish (62 samples) caught in the Shulba reservoir, tributaries, and the Irtysh River bed within the East Kazakhstan region, Zaisan Lake in the Kurchum coast was carried out. We found that the content of Sr⁹⁰ [min 5.34; max - 20.76 Bq/kg] exceeded the content of Cs¹³⁷ [min - 0.43; max - 2.96 Bq/kg] in hydrobionts caught in the Irtysh River, which may be associated with the peculiarities of circulation of each radionuclide in the environment, as well as the possibility of creating colaborative links between radionuclides and organic substances. Monitoring of hydrobiota radioactivity in field and artificial conditions is an important condition for the development of fish farming enterprises to ensure national food security and to create export potential of the Republic of Kazakhstan.