The article presents an analysis of changes in the chemical composition of water in the oligotrophic Lake Munozero for the period from 1959 to 2019. The lake is located in the upstream part of the Konchezero lake-river system (Munozero, Pertozero, Gabozero, Konchezero, Ukshezero). The Konchezero group of lakes is among Karelia’s unique water bodies. Of all the lakes in this group, Lake Munozero stands out for its high mineralization (100 mg/l) and low content of organic matter (Corg = 2–4 mg/l) and nutrients. Lake Munozero water features a low color index (20–30 degrees) and high transparency (4–5 m). This lake is one of the best water bodies in Karelia in terms of potable water quality. The article gives an account of the changes that have occurred over the past 60 years in the ionic composition of lake water, the content of nutrients, and the oxygen regime under the impact of both natural (climate change) and anthropogenic factors.