We've been following rivers through Germany, mostly since there are well marked routes and it's pretty flat (it's especially nice to follow one downstream since that's also mostly downhill).
We were familiar with the parts of the Rhine near Düsseldorf and Köln, filled with barges laden with shipping containers. But the big industry soon melted away and there's been surprising variety in the landscape...
We passed through the German wine district with vineyards going up the steep river banks and medieval castles on every high point. We have found ourselves biking through forests and fields of asparagus, strawberries, wheat and potatoes (etc, etc). The Donau (aka Danube) river has practically no boats, probably due to the regular hydroelectric dams.
We'll continue following the Donau for a few more days in Germany, then through Austria to Vienna.