Neil, Weihlac, thank you very much for this. I have read many of the earlier posts about water levels affecting the ability of ships being able to transit rivers. I didn't realize when I posted that damage to a lock could also affect water levels. Eek!Viking ships draw ~5.5' of water. Other cruise lines have newer ships that draw ~4.5' of water. That seemingly small difference means some ships can navigate the low water levels and Viking can't. We encountered this issue last fall with another river cruise provider where our ship made every port as scheduled, and people on Viking ships on the same itinerary were bussed from ship to ship because the Viking ships could not go through the areas with low water. The Viking passengers were not happy, to say the least. Instead of the advertised "unpack once for the entire trip" they were packing and unpacking every day or two.
Having said this, a river cruise is a GREAT experience. Just choose your tour/ship operator carefully, using the services of a river cruise travel expert.
Here is some info about the river water levels last year. The problem comes and goes.