[en] Dissolved gaseous mercury (DGM) and total mercury (TM) concentrations were measured in Juam Reservoir, Korea. DGM concentrations were higher in spring (64 ± 13 pg L^-1) and summer (109 ± 15 pg L^-1), and lower in fall (20 ± 2 pg L^-1) and winter (23 ± 6 pg L^-1). In contrast, TM concentrations were higher in fall (3.2 ± 0.1 ng L^-1) and winter (3.3 ± 0.1 ng L^-1) than in spring (2.3 ± 0.1 ng L^-1) and summer (2.2 ± 0.4 ng L^-1). DGM concentrations were correlated with water temperature (p < 0.0001), ORP (p < 0.0001), UV intensity (UV-A: p = 0.008; UV-B: p 0.003), and DOC concentration (p = 0.0107). DGM concentrations varied diurnally with UV intensity. The average summer DGM (109 ± 15 pg L^-1) and TM (2.2 ± 0.4 ng L^-1) concentrations in Juam Reservoir were higher than the averages for North American lakes (DGM = 38 ± 16 pg L^-1; TM 1.0 ± 1.2 ng L^-1), but lower than levels reported for Baihua Reservoir in China. - The first seasonal measurements of DGM and THg concentrations in a Korean reservoir