Freshwater lakes, as accumulators of substances from their catchment areas, are vulnerable to internal nutrient and toxic loads caused by shifts in redox conditions at the water-sediment interface. Based on synchronized data on the chemical and particle size distribution of catchment soils, sediments, and the hydrochemical characteristics of water masses in 38 lakes in the Republic of Tatarstan, a two-loop model for regulating the redox regime of water bodies has been proposed and verified. The model includes a dynamic redox circuit regulated by post-sedimentation processes of transformation of labile organic matter, and a stabilizing sorption circuit associated with the accumulation of stable organic matter (humus) and clay particles of terrigenous genesis in bottom sediments. Using hydrochemical indicators (NH₄⁺/NO₃^‒, ХПК/БПК₅, концентрации O₂, Fe, Mn, PO₄^3‒ concentrations), four phases (zones) of the oxidation-reduction state of the system were formalized – from aerobic to sulfate-reducing. The Random Forest method established that the position of a reservoir/its section in the described phase space is predicted with high accuracy (R² = 0.91, accuracy = 0.89) by only four stable parameters: the content of organic matter in bottom sediments (the activation vector of redox processes), the content of fine particles in soils of the catchment area (the stabilization vector), as well as the content of nitrogen in soils and clay particles in sediments. The results substantiate a transition from reactive water quality monitoring to proactive management of catchment factors, and open up opportunities for quantitative prediction of the resilience of lake ecosystems to eutrophication and secondary pollution.