The results of numerical experiments by definition of propagation zones Cs137 in the Kara Sea in case of a radiological contamination offset from the estuary Ob are tendered. The stationary source of a radioactivity dumping was set in surface layer of river and seawaters mixing zone in the Ob Bay. The modeling was carried out on the basis of a numerical solution of the three-dimensional equation of passive impurity transport with turbulent diffusion and with allowance for of processes of a half-decay and sedimentation on suspension. The equation was considered concerning total concentration of a radioactive impurity in seawater (in dissolved state and suspended matter). The assumptions of a stationarity of concentrations Cs137 ratio in different states and constant suspended matter distribution in water column were done. The part of radionuclides content in suspension from total radionuclide content was set in particular coefficient p on the basis of nature measurements. As a result simulation we obtained the predominant transfer Cs137 in northern and north-east direction from an estuary Ob and the sufficiently strong dependence of the scales of propagation on the coefficient p.