This 2013 video from Denmark is called The Houting Project.
Translated from Dutch NOS TV:
Joint German-Dutch research proves this.
Houting originally lived around the Baltic Sea and North Sea, and almost became extinct.
Only in the small Vida river in Denmark houting still lived.
They became extinct in the Rhine about 1930.
Germam researchers in 1992 put them back into the Lippe, a tributary of the Rhine.
In the Netherlands. they spread to rivers, coastal waters, and around the IJsselmeer.