Half a millennium of mercury production at Idrija is reflected in increased mercury contents in all of its environmental segments. Stream sediments have been monitored along the Idrijca and Soča rivers (70 km) every 5 years since 1991. It has been discovered that there was no decrease in mercury concentration in stream sediments during the last 15 years. Upstream from the town of Idrija, mercury concentrations in active river sediments vary from 1 to 10 mg/kg dry weight (average 3.3 mg/kg). From Idrija to Spodnja Idrija mercury concentrations increase extremely and vary greatly. The average in this area amounts to 603 mg/kg with individual contents up to 4121 mg/kg. From Spodnja Idrija to the Idrijca-Soča confluence the average is 213 mg/kg, while the average in the Soča river sediments is 57 mg/kg. Floodplain soils and samples of averaged meadow forage and plantain (Plantago lanceolata) were collected on river terraces at two localities in the lower course of the Idrijca. It has been determined that floodplains along the Idrijca River are strongly enriched with mercury. The average concentration of Hg in the upper 20 cm of the floodplain at IDB location is 157.7 and at TEM location it is 294.8 mg/kg. Samples of averaged meadow forage and plantain contain from 0.055 to 0.220 mg Hg/kg. In comparison to the plant samples from Idrija in the 1970s, these contents are relatively low. However, regarding mercury contents in plants in non-polluted soils the contents on the Idrijca River terraces are considerably higher than the background.