Using the example of the rivers of the boreal zone of the Far East of the Russian Federation, it is shown that the dynamic light scattering (DLS) intensity is proportional to the content of large colloidal particles (0.05–1.0μm) in the filtrates obtained in the process of water preparation for chemical analysis. Accordingly, the DLS method can be used to characterize the content of large colloids in river waters, assess the efficiency of colloid separation from suspended particles, and control membrane clogging during filtration. A significant direct correlation was found between the DLS intensity 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 DLS intensity of filtrates on the mass content of large colloids in them. A significant, but less strong relationship is observed with REEs, Th, and other hydrolysates (Zr, Hf, Sc, Ga), in the balance of which large colloids can also play a significant role in the river waters. The concentration of chemical elements for which dissolved forms of migration prevail (major cations, Li, Sr, Ba, Mo, U) or small colloidal forms (DOC, Cu) do not show any connection with the intensity of DLS in filtrates. Information on the content of large colloidal particles in filtrates, obtained by the DLS method, allows us to better understand the causes and scales of spatial and seasonal variability of the concentration of a number of hydrolysatrs (Fe, Al, Ti, REEs, Th, etc.) in river waters, as well as to control the possible influence of filtration artifacts on the results of chemical analysis of waters.