List of tributaries of the Danube
The Danube is Europe's second-longest river. It starts in the Black Forest in Germany as two smaller rivers—the Brigach and the Breg—which join at Donaueschingen, and it is from here that it is known as the Danube, flowing generally eastwards for a distance of some , passing through several Central and Eastern European capitals, before emptying into the Black Sea via the Danube Delta in Romania.
Dikerogammarus villosus
"D. villosus" was originally found in the lower courses of large rivers in the Black Sea and Caspian Sea drainage basins. It has become an invasive species across central and western Europe, using the Danube river and its tributaries in its expansion. It is thought to have first escaped from the Danube in 1992 when the Rhine–Main–Danube Canal was opened and has since spread to nearly all the major rivers in western Europe, including the Rhône, Loire, Seine, Moselle, Meuse, Rhine and Main, as well as the Baltic Sea. It is unknown how the species is dispersed but it is probably related to shipping activity. It spread quickly through western Europe; found in the Rhine at the German–Dutch border (1995), the canals and rivers of northern Germany (1998), the Baltic Szczecin Lagoon (2001), the Moselle (2001), the Netherlands (2002), Lake Constance (2003), Lake Leman, the Rhine in France (2003), the (2003) and Lake Garda (2003). Its spread is thought to be related to the previous introduction of the zebra mussel, "Dreissena polymorpha" which it has evolved alongside. In September 2010, it was found in Grafham Water in Cambridgeshire, the first report of the species in the United Kingdom and it was found in Wales in November 2010.