I'd like to take a river cruise from Vienna to Budapest, and visit Prague before or after. What time of year would ensure passage by water, rather than bus, due to low water? Does anyone have first hand experience with any of the many river cruise companies in Europe? I'd like this to be a spectacular vacation, and can't seem discern the differences among the many offerings! Thank you in advance for any advice.

Most 1 week cruises go from Passau to Budapest and back. They are usually popular with elderly people.
Summer is the warmest season and therefore more pleasant for a cruise. In September and October, fog cannot be excluded. May is either fine or very rainy. But the weather is unpredictable all the year round in this area.

There is usually no low water in spring and early summer.

I suppose you know that there are also some smaller boats (with no cabins) between Passau and Linz as well as between Linz and Vienna that you can board or leave at all intermediate stops.

Is low water really a problem? I would think high water in the spring, making bridges too low for the boat to fit underneath.

Anyway, looks like early summer is the best bet

Uniworld gets the best reviews of the river cruise companies.

Go to the cruise forum here and read the dozens of reviews of cruises that were really bus trips.

Thank you, everyone! This is helpful information!

You might actually consider going to www.cruisecritic.com and looking at reviews there. The site has many, many more reviews than you are going to find here.

And what constitutes a "great" or even a "good" review is subjective at best IMO. Uniworld may get "the best reviews" but I can tell you from personal experience we did a European river cruise with another company and were more than just pleased with the results.

There are several factors to consider including the layout of the vessel, it's amenities, the entertainment, food quality, the itinerary, etc., etc.

But I also realize there seem to be certain people on this site whose opinions are considered to be absolutely infallible and I am not one of them. I'll simply say I hope it works out for you.

We encountered heavy rains on a Danube river cruise from Nuremberg to Budapest in late May, early June a few years ago.

Yes, it's europe north of the Alps and you can get any weather at any time. And spending any 7 days in that area is likely to have at least one rainy day - since the area is not a desert.

Low water has been a huge issue in late summer and early fall in recent years.

This is what turns cruises into bus trips. How the cruise line handles this is a key determinant in how happy people are with the trip.