Final answer:
The Danube River is the waterway that flows through or borders Germany, Austria, Slovakia, Hungary, Croatia, Serbia, Bulgaria, Moldova, and Romania, eventually draining into the Black Sea.
Step-by-step explanation:
The river that passes through or touches the borders of Germany, Austria, Slovakia, Hungary, Croatia, Serbia, Bulgaria, Moldova, and Romania is the Danube River. It is one of Europe's major rivers and provides an essential route for transportation and trade.
Originating in the region of southern Germany, near the border with Switzerland, the Danube flows east through major European cities such as Vienna, Budapest, and Belgrade before emptying into the Black Sea.
The Danube is also linked to the Rhine River via the Main-Danube Canal, which has made it a significant corridor for both economic activity and the movement of species between different aquatic ecosystems.