 Among these are an exceptionally high diversity of sturgeon, a total of six species (beluga, Russian sturgeon, bastard sturgeon, sterlet, starry sturgeon and European sea sturgeon), but these are all threatened and have largely–or entirely in the case of the European sea sturgeon–disappeared from the river.The huchen, one of the largest species of salmon, is endemic to the Danube basin, but has been introduced elsewhere by humans.Important tourist and natural spots along the Danube include the Wachau Valley, the Nationalpark Donau-Auen in Austria, Gemenc in Hungary, the Naturpark Obere Donau in Germany, Kopački rit in Croatia, Iron Gate in Serbia and Romania, the Danube Delta in Romania, and the Srebarna Nature Reserve in Bulgaria.