To assess the present day quality of the surface and ground water and its changes due to anthropogenic impact NWPI KRC RAS has carried out mapping of Karelian surface waters relying on a complex of parameters (Fig.2). The main chemical parameters used to assess the water quality were: pH, content of organic matter, iron (Fe), total phosphorus (Pt), chlorophyll (Chl "a") and oxygen (O2). Natural water quality was determined for the waterbodies preserved in their natural condition. Also considered were regulated waterbodies and the water objects with forest drainage carried out in their catchment areas. Fig.2 shows contaminated waterbodies where sewage is discharged, the recorded indices differ from the natural ones and which are possibly contaminated with toxic substances, together with the waterbodies of the close to the natural status. All water bodies in heavily paludified areas (the White Sea lowland, upper reaches of the Shuja river, rivers Vyg, Niukhcha, etc.) as well as small lakes located in river divides and acidified by anthropogenic activities (Chuchjarvi, Kivijarvi, etc.), and highly eutrophied lakes (Kroshnozero, Svyatozero, Kotkozero, Pjalozero, etc.) can be classed as waterbodies with low-quality water.