Natural water bodies located in different geographical regions of Russia vary widely in hydrochemical indicators of water quality. Despite this, unified federal water quality standards (MPCs) have been established for the entire territory of our country, without taking into account the formation process of quantitative and qualitative indicators of water quality in water bodies or respecting the natural uniqueness of the basins in which they are formed. The assessment of the surface water quality on the basis of federal maximum concentration limits completely ignores not only the specific and unique features of catchments but also their natural diversity. A collision arises when the concentrations of certain compounds do not interfere with the stability of the existing biocoenoses but fail to meet the maximum permissible concentrations for reservoirs used for fisheries (MPC), which apply to almost all water bodies in Russia. The purpose of this study is to substantiate the regional concentrations of metals in Lake Pskovskoye. The relevance of the study is due to the need to improve the MPC system for Lake Pskovskoye, which has a fishery
value. The calculations were performed with hydrochemical monitoring data for the period 2000–2021. The results of the calculations of regional maximum permissible concentrations
(MPCREG) for six metals (total iron, copper, lead, manganese, cadmium, zinc) are presented. Three different methods were used for the calculations: suggested by S. A. Patina, by D. G. Zamolodchikov, and by E. V. Venitsianov and co-authors. Calculations by Patina’s method involve two attributes - the average concentration of a chemical element for the period under review and the standard deviation. Calculations by the method of D.G. Zamolodchikov were based on the upper and lower quartiles of the distribution. The method of E.V. Venitsianov and co-authors employs three attributes - the sample size, the upper quartile of the distribution, and the standard deviation for the quantile of about 0.75. Proceeding from the principle of sanitary maximalism, we argue that the optimal method for calculating metal MPCREGs is the method suggested by E. V. Venitsianov and co-authors. The regional maximum permisslbe concentrations of metals in Lake Pskovskoye proved to tightly correlate with their clarke numbers in the earth’s crust.