The Biesbosch (from "bies", "rushes", and "bosch", "woodland") is an area southwest of Dordrecht formed when the dike on the Meuse burst and the St. Elizabeth's floods on 19 November, 1421 engulfed great tracts of land in the southwestern Netherlands and altered the geography of the whole area, inundating over 40,000 hectares/100,000 acres of land. More than four-fifths of the flooded land has been reclaimed since the 18th century. An area of 6,000 hectares/15,000 acres was left as it was, and now forms the Biesbosch nature reserve and bird sanctuary.