This is a post I did after a visit in 2011.
There were a lot of cruise boats on the Danube but not many barges. I was surprised that there was not more freight traffic.
Past flood levels. Note the level for 2002. Many places on the Danube got flooded that year.
Passau is an attractive place for a few nights stay. There is a large pedestrianised area with shops, restaurants and bars. A lot of Danube cruise boats moor at Passau. There are also lots of cyclists about because the Danube Cycle Path passes nearby.
Regensburg is not too far away and is also worth a few nights stay. I liked it as well as Passau.