Throw your fortune into the floods

This plastic displays how Hagen sinks the Nibelung treasure. The sculpture is on the banks of the Rhine river in Worms, Germany.

According to the saga (Nibelungenlied) Hagen threw the treasure of the Nibelungen somewhere in the Rhine, and has never ever been found.
A bit silly to throw a treasure in a river, there are better ways to dispose of something so valuable. Even 1000 years ago.

And, as this is a saga, it is a story based on true circumstances, but usually not more than that: based on. As a whole they are not true. It would be silly to believe that Hagen, if he was real, would have thrown a treasure away, for whatever reason.