Rivers draining the acid sulphate soils of western Finland deliver large amounts of metals (e.g. Cd, Co, Cu, La, Mn, Ni, and Zn) to the coastal sea. To better understand metal enrichment in the sea floor, we analysed metal contents and grain size distribution in nine sediment cores, which increased in the 1960s and 1970s and stayed at high levels afterwards. The enrichment is visible more than 25 km out from the river mouths. Organic aggregates are suggested as the key seaward metal carriers.