Short sediment cores (up to 44cm long) taken from salt marshes regenerated during the last 60years in the Urdaibai Biosphere Reserve have been interpreted on the basis of microfaunal and geochemical determinations and historical data. Agricultural soils in the middle and upper estuary reaches were abandoned during the 1950s and entrance of estuarine water provoked a rapid natural environmental transformation of these anthropogenic areas. Increasing amounts of sand and benthic foraminifera were deposited at a very high sedimentation rate (average 16mmyr -1 ) during the 1950s and 1960s allowing well developed regenerated salt marshes to be rapidly established in these formerly occupied areas. During recent decades much lower sedimentation rates (average 2.5mmyr -1 ), abundant agglutinated foraminiferal assemblages and enrichment of heavy metals (Pb, Zn, Cu, Ni and Cr) due to industrialization are characteristic of these already regenerated environments. This rapid regeneration process (less than 10years) is of great interest for environmental management of modern coastal zones where extensive reclaimed land could be easily restored to tidal wetlands under the current scenario of accelerating sea-level rise. © 2011 Elsevier B.V.