What happens when European rivers get too low for river cruises to pass? All too often it means forcing passengers onto a bus to catch up with their ship elsewhere.
And despite the lack of control the companies have over Mother Nature, it also often translates into some very angry, disappointed passengers.
After a perfect 2017, this year's brutally hot and dry European summer was a reminder of the complicated logistical problems river cruise companies face in low-water years, both in trying to make itinerary changes as painless as possible and also in communicating them to passengers.
Since water levels can change from day to day, it can be nearly impossible to alert guests before they arrive that their itinerary might be altered or that their trip may involve bus transfers or even swapping ships.
Companies say they work to inform agents and guests of potential issues and do their best to keep to planned itineraries.
For instance, when ships couldn't get into Budapest for a few days in August, AmaWaterways put guests waiting to embark in a hotel overnight while finding another vessel to ensure they didn't miss the traditional, must-see nighttime illumination cruise past the famed Hungarian Parliament Building. The next day, guests were bused to Vienna to begin their cruise.
Policies for informing guests and agents in advance of potential issues vary widely, in part because of the fast-changing nature of river levels.
"We always proactively share updates to guests and partners, and in most cases, for the limited number of cruises that had been impacted, we were able to seamlessly alter small sections of the trip to offer an equally rewarding itinerary," Uniworld Boutique River Cruise Collection said in a statement.
Experienced agents say it's important for those who sell river cruises to know the rivers and to advise clients before and after they book about potential weather-related problems.
Karimah Dossa, vice president of Hill Barrett Travel in Woodinville, Wash., said her agency briefs all of its clients at the time of booking and then again two weeks before they leave.
Tauck, she said, sends out an automatic email to its clients a month before their sailing to warn that water levels are a day-by-day thing.
Diana Hechler, president of D Tours Travel, said she has never been notified of a low-water situation in advance of a client's departure but said she has been "lucky that my clients have not been seriously affected by this issue."
"It seems that it is the Danube sailings that are most commonly affected," she said. "I certainly advise Danube passengers that there is always a risk. In addition, I usually promote the Rhine or Seine or the Provence itineraries for first-time river cruisers."
In other words, Hechler said, agents need to be aware of the rivers where problems are most likely to happen and to pick their clients' itineraries carefully.
"If the itinerary is really screwed up and the cruise itinerary is seriously affected and these are first-time river cruisers, they might never choose another river cruise," she wrote in an email. "For a repeat client, it might be viewed as an insignificant blip."
A chance to impress guests
Indeed, not all passengers get upset by changes.
AmaWaterways president Rudi Schreiner shared an email from one couple who, recognizing the logistical hoops the company had to jump through when it had them swap ships midsailing, called their experience the "holiday of a lifetime."
He said it happened on the company's first ship swap of the season, when the sister ships AmaPrima and AmaCerto were going in opposite directions, one from Amsterdam to Budapest and the other from Budapest to Nuremberg, Germany, and water levels prevented them from crossing the upper Danube.
The crews went into high gear, cleaning cabins and swapping out luggage while the passengers went out on excursions to Salzburg, Austria, from nearby ports. The guests came back to the same cabins on different ships in different ports to resume their sailings.
"We will forever compare future vacations to our time with AmaWaterways: You are our new standard of excellence," the couple wrote to the company.
Senior editor Jamie Biesiada contributed to this article.