The results of a study of Lake Tikshozero ecosystem are reported for the first time. Its hydrological, hydrochemical and hydrobiological characteristics were analyzed. The lake is of glacial genesis and belongs to the White Sea drainage basin. Human population in the catchment area is minor, and there are no large-scale industries. Analysis of the chemical composition of water samples has shown that the water belongs to the calcium group of the hydrocarbonate class, is poorly mineralized (27 mg/l), and has a colour index of 103–115°. The water has a near-neutral active reaction, its рН is 6.0–6.4, the permanganate index varies from 11.8 to 13.0 mgО2/l, and BOD5 is 1.8 mg/l. The lake is classified as mesotrophic, based on the mineral nitrogen concentration dominated by ammonium and nitrate nitrogen. The quantities of zooplankton indicate that the pelagic zone of the lake is of the oligotrophic type with biomass up to 1.0 g/m3 (low class), and the littoral zone isof the transitional α-mesotrophic – β-mesotrophic type with biomass ca. 2.0 g/m3 (moderate – medium class). The development level of the benthic fauna, in which chironomids are dominated by the subfamily Chironominae, shows that Tikshozero is an α – mesotrophic lake. Judging by the chironomid index “K” of 1.76, the lake is mildly polluted. Seven fish species have been captured from the lake. Tikshozero is inhabited by valuable fish species (whitefish and vendace) and has the highest industrial-fishing status. The results of the study will be taken into account when developing the database of Karelia’s freshwater ecosystems, which will provide a background for monitoring the environments strongly affected by human activities.