The ease with which radionuclide moves through the environment and is taken up by plants and animals is determined by its speciation and site-specific environmental characteristics. The peculiarities in climate, geomorphology and ¹³⁷Cs speciation in the fallout were demonstrated to lead to differences in migration rates of ¹³⁷Cs in the environment and rates of its natural attenuation. It has been revealed that in the exclusion zone the Fukushima-derived ¹³⁷Cs is strongly bound to soil and sediment particles, which reduces potential bioavailability of this radionuclide. Substantial fraction of the deposited ¹³⁷Cs on soil of the exclusion zone were found to be incorporated in hot glassy particles (“Cs balls”) insoluble in water. These particles are decomposing in the environment essentially slower as compared with Chernobyl derived fuel particles. Wash-off from the slopes of contaminated catchments and river transport are key long-term pathways for radionuclide dispersal from contaminated areas after the Fukushima accident. The climate conditions for the Fukushima Prefecture of Japan are characterized by higher annual precipitation (1300-1800 mm/year) with maximum rainstorm events during typhoon season. Typhoons Etou in 2015 and Hagibis in 2019 demonstrated the substantial redistribution of ¹³⁷Cs on river watersheds and floodplains and in some cases natural self-decontamination occurred. Steep slopes of Fukushima catchments are conducive to higher erosion and higher particulate r-Cs wash-off. Irrigation ponds in Okuma and Futaba towns demonstrated persistent behavior of ¹³⁷Cs similar to the closed lakes in Chernobyl, its concentration is decreasing slowly and showing regular seasonal variations: the ¹³⁷Cs concentrations tend to grow in the summer and decrease in the winter.