Pick your time of the season to cruise the rivers, and do not expect to cruise the Elbe after mid June, but do expect to pay a lot for a very small room as you travel by bus to see what was formerly East Germany.
We had previously enjoyed Viking cruises on the Rhine and Rhone. The summer of 2015 saw insufficient water in the Elbe for Viking to cruise successfully after midJune. We became aware of the problem after reading reports on the Internet. We were NOT alerted to the problem by Viking. In mid July I called the service line and discussed the issue with the Viking rep, who was very noncommittal and expressed hope that rain would fall and fill the river. I learned from reading on the Internet that a succession of angry travelers had discovered that the "cruise" would be a bus trip after they had checked in to the hotel in Berlin in late June and July .
Most of the comments expressed displeasure at not being told of the doubtful state of affairs prior to arriving at the embarcation point. A few had discovered the problem earlier and had contacted Viking before leaving home, and were told they could cancel without penalty. Viking did not offer this option to me until I asked point blank about it, and was told that in fact I could cancel.