Abstract Stream and flood plain sediments along the valley of the Idrijca River were systematically sampled. Upstream of the mercury mining town of Idrija, the Hg in stream sediment varies around 2 mg/kg. Mecury contents in the region from Idrija downstream to the town of Spodnja Idrija are from 100 to 1, 000 mg/kg. Downstream from Spodnja Idrija, sediments contain lower Hg (from 5 to 300 mg/kg). Recent overbank sediments are enriched relative to the stream sediments downstream of Idrija. River flood plain sediments that represent an accumulation of polluted sediments have Hg contents of 100 to 200 mg/kg.