Humic substances (humic and concern to basic complexing ligands of humid zone natural waters. Forming strong complexes with metals, dissolved in water, they, on the one hand, reduce metals toxic influence, and on the other hand they raise migration ability of the above mentioned elements. High content of humic substances usually coincides with 90Sr significant volumetric activity in surface waters of the Chornobyl Exclusion Zone. This fact can be explained by strontium washing out in the structure of complex compounds with humic substances from catchments surface