Beluga sturgeons live in the Black Sea and can grow up to 8 m in length. As recently as the 19th century they would swim upstream to reproduce. In the Danube this migration even took them as far as Regensburg – 2000 km from their natural habitat. Large numbers of them were hunted during this journey for their meat and especially for their valuable caviar. The construction of hydroelectric power plants along the Danube also prevented them from migrating upstream. Today the beluga sturgeon is threatened by extinction.