Anthropogenic activities are often considered to be the main sources of mercury (Hg) found in aquatic systems. The aim of this study was to reconstruct the historic input of Hg to a large lake (Lake Ekoln) situated downstream the City of Uppsala using a dated sediment core. The main objective was to reveal general long-term (millennia-scale) trend in mercury loadings to the lake assess to what extent the lake has received an increase input of mercury during the last century from atmospheric inputs or local sources (mining activities, hospital effluents, industries or agricultural activities). Sediment samples were analyzed with X-ray fluorescence spectroscopy for measurements of lead and phosphorous (used as a proxy for atmospheric inputs and effluent water, respectively). Total Hg was analyzed using a mercury analyzer. My results indicate high Hg concentrations in sediment of Lake Ekoln during the last three centuries. Hg concentrations was not correlated to atmospheric derived metals (Pb) or effluent water derived nutrients (P) and only weakly correlated to the organic matter content of the sediment. Highest concentrations was found during a period around 1850 and in the last few years. The weak correlation with Pb suggest that the Hg is entering the lake from other sources than atmospheric inputs. The most likely local sources are argued to be mining activities (including fossil fuel burning during the production of iron) or Uppsala university hospital situated upstream of Lake Ekoln. However, there is a large uncertainty regarding the importance of these historical Hg sources for the lake.