This 2011 video says about itself:
The European beaver (Castor fiber) was hunted almost to extinction, both for fur and for castoreum, a secretion of its scent gland believed to have medicinal properties. However, the beaver is now being re-introduced throughout Europe. Several thousand live on the Elbe, the Rhône and in parts of Scandinavia. In northeast Poland there is a thriving community of Castor fiber. They have been reintroduced in Bavaria and The Netherlands and are tending to spread to new locations.
Translated from the Dutch ARK Natuurontwikkeling conservationists, 7 February 2016:
After more than two hundred years of absence about twenty years ago beavers emerged spontaneously in Limburg province. These were some individuals from Germany. Their number was too small, and mutual distance too large to form a viable population within the foreseeable future. Therefore thirty beavers were freed in the region between 2002 and 2004. There was enough habitat by river restoration and nature reserve management in the Meuse Valley. Meanwhile beavers live, with numbers estimated at five hundred animals, in nearly the whole of Limburg. In wet, wooded nature beavers play a key role.