At least 20 river cruises have been affected in Germany on the Danube and Elbe rivers after lower than normal water levels have forced some cruise lines to undertake complex logistical maneuvers to keep tours running. Some Cruises have had to alter their itineraries. Cruise Critic will continue to monitor water levels in the regions and update you with further reports. Viking Cruises has seen more than a dozen of its itineraries affected, and maintains an updated list on its website. In addition to "ship swaps" -- where the line undertakes a passenger exchange (usually via bus) between two ships positioned on either side of an impassable stretch of river -- at least one cruise has been more severely affected.