Viking River Cruises and TUI have both warned customers of potential changes to itineraries, with recent reports of two ships running aground. River cruise holidays in Europe face disruptions and itinerary changesViking River Cruises, in a statement on its website, said: "Sections of the Danube and Rhine Rivers are currently experiencing exceptionally low water levels. "As a result, select Viking river itineraries may be modified. "This approach helps minimise overall disruptions and preserve the experience our guests expect from Viking." Do you have a river cruise holiday in Europe booked?