Viking Forseti first ran into the back of another ship in a lock four days into the cruise, causing it to miss time slots for the locks which led to even more delays.
It was then involved in a second accident -- in which another ship ploughed into it.
No passengers were hurt in either incident, but both caused long delays and required inspections by authorities.
There were also lock strikes along the Danube yesterday, which have been going on intermittently all summer and which caused further delays to the cruise.
Member DIST-THDR has been posting on the Cruise Critic Message Boards:
"my wife and I are at this moment on the Viking Forseti. On our 4th night out our ship ran into the back of another causing us an 18hr delay, missing our time slots for the locks which led to even more delays, then was involved in another collision,(more delays) and since we have been bused to every port stop since, on the average 1-1 1/2 hr each way. we are still behind by a day getting to Vienna and onward to Budapest. 80% of passengers upset and protesting the problems. Now we have to deal with rotating lock strikes and not sure what is going to happen the rest of the way to get us to Budapest on time."
Viking has confirmed that both incidents took place and a senior executive at the line has written a personal letter to all those affected.
A Viking spokeswoman confirmed: "Viking Forseti was involved in two minor collisions during its current sailing. No passengers were injured, but the itinerary did need to be slightly modified to account for an inspection afterward. Coincidentally, this sailing was also affected by a German lock workers' strike, causing further delay.
"The ship is now underway again, and Viking is working to adjust several elements to make up lost time and ensure that the remainder of the journey is seamless and enjoyable. To that end, passengers will be treated to several complimentary amenities along the way, and Viking customer service will be following up individually with passengers upon their return home."
Last month an AmaWaterways' AmaDagio was involved in an accident in a lock, which caused numerous knock-on delays.
--By Adam Coulter, U.K. Editor