The poorly recultivated tailings at the R. Ore Mines Co. site also contain large amounts of pyrite. Owing to oxidation and acidification processes triggered by oxygen-saturated acid rain, heavy metals are transported by the leachate via the groundwater to surface streams of high buffering capacity where the metals are precipitated within a brief period of time. The recipient Parádi Tarna is contaminated indirectly over the tributary Bikk stream. The solid metal compounds bonded to iron(III) hydroxide settle out over a short distance (a few km) in the bed of the Parádi Tarna. At times of low and medium streamflow the heavy metals impose no restriction on the use of Parádi Tarna water for irrigation. However, flood waves caused by periodic releases of temporarily stored mine drainage water, or by major rains stir up the, metal contaminated bottom sediment and transport it to the lower stream sections. In these periods the Parádi Tarna is unfit for irrigation.