Hg concentration was studied in waters of 16 lakes in the Suwałki Landscape Park. The samples of lake water were collected from the surface zone and I m above the bottom, in the deepest site of the lakes. Apart from Hg concentration, the measurements included: the pH, soluble oxygen, water saturation with oxygen, electrolytic conductivity and total hardness of water. Hg concentration varied from lake to lake, but remained at the same levels in consecutive years. It has been found that Hg concentration in the bottom zone is higher than that in the surface zone. Significant differences were found between mean Hg concentrations in the bottom zone both during the summer and winter stagnation. No significant differences were found in mean Hg concentration in surface waters in different seasons of the year.