Abstract: The δ²H and δ¹⁸O values of the atmospheric precipitations in the Khibins vary within the range –147 ≤ δ²H ≤ –37‰, –20 ≤ δ¹⁸О ≤ –4‰ and are close to the global line of the precipitations for the northern hemisphere; the light values (with a positive deuterium excess) are typical of snow, while the heavy values are typical of rains. The data on the isotopic composition of water in open water bodies and groundwaters suggest their formation from the precipitations. Their flow (and subsurface migration) is accompanied by mixing of snowmelt and rain water; the efficiency of mixing can be evaluated by a decrease in the variation range of the values of δ²H and δ¹⁸О. According to isotopic data, the water of Lake Imandra, the major water body in the region, has formed through mixing of snowmelt and rain water in a proportion close to 1 : 1.