Abstract <p>Boreal rivers of the Far East of the Russian Federation were analyzed to show that the intensity of dynamic light scattering is proportional to the concentration of large colloidal particles (0.05–1.0 μm) in filtrates obtained during the preparation of water for chemical analysis. This shows that the dynamic light scattering method can be used to characterize the content of large colloids in river waters, to assess the efficiency of separating colloids from suspended particles, and to control membrane clogging during filtration. A significant direct correlation was found between the intensity of dynamic light scattering of filtrates and the concentration of Fe, Al, and Ti in them in accordance with the maximum affinity of these metals to large colloids. This confirms the dependence of the intensity of dynamic light scattering of filtrates on the content of large colloids in them. A significant but weaker relationship is observed with rare earth elements, Th, and other hydrolysate elements (Zr, Hf, Sc, and Ga) in the balance of which large colloids can also play a significant role in the river waters of the region. The concentration of chemical elements for which dissolved migration forms (macroions, Li, Sr, Ba, Mo, and U) or small colloidal forms (dissolved organic carbon, Cu) prevail does not show a relationship with the intensity of dynamic light scattering in filtrates. Information on the content of large colloidal particles in filtrates, obtained by the dynamic light scattering method, allows for a better understanding of the causes and scales of spatial and seasonal variability in the concentration of a number of hydrolysate metals (Fe, Al, Ti, rare earth elements, Th, etc.) in river waters, as well as for monitoring the possible influence of filtration artifacts on the results of chemical analysis of waters.</p>