Rivers are an increasingly popular, care-free way to tour Europe. And yet—like all other travel—they’re subject to nature’s whims, as we saw this summer, when parts of the Elbe and Danube were affected by drought-induced low-water levels. This sort of curve ball can upend everything from touring to whether a ship can sail at all.

So what do you do if you spent $3K on your first (maybe only) river cruise, and find out two weeks before you leave that the itinerary may change due to water levels?

Here’s what you need to know.

When and where water-level disruptions are most likely to occur

First, note that all rivers are subject to water-level fluctuations, and the number of cruises actually impacted is small.

In general, water levels affect roughly 5 to 10 percent of cruises; and when they do, it’s usually for limited portions of the route—often those that lack manmade controls, such as the Danube between Regensburg and Passau in Germany.

Low water levels typically occur in mid-to-late summer—especially if it’s been severely hot and dry, as it was this summer. In Europe—where the vast majority of river ships are positioned—conditions like those recently on the Elbe and Danube last occurred in July/August 2015.

High water levels/flooding are more likely in spring, when snow melt and seasonal rains feed rivers, making it difficult for ships to navigate unpredictable currents through locks and beneath bridges. This hasn’t happened in Europe since 2013.

The most reliable time of year to cruise Europe’s rivers is fall, when the weather is more stable—but again, nothing is guaranteed.

Cruise lines are prepared for and address water-level issues; be sure to read the fine print

Because water levels can be a wild card, cruise lines outline the possibility of changes or cancellation in the fine print of most contracts (usually under an “Acts of God” clause) and in FAQ sections on their websites. If, nearing your departure date, it looks like water levels will be an issue, most lines will alert passengers via email and online notifications.

Still nature can throw curve balls, forcing cruise lines to make last-minute adjustments. “Each river is unique and presents different challenges and solutions. With water levels, they can be a bit unpredictable and we adapt on a week-to-week basis,” explained Michael DaCosta, Manager of Marketing and Sales for North America for CroisiEurope, which operates 32 river ships in Europe.

Stay informed by monitoring emails and communication as your departure nears.

If it looks like your cruise will be affected, your options are often limited

River cruises aren’t cheap, so it’s natural to stress over the idea that your trip might be canceled or turned into a bus tour. But water levels can change dramatically and quickly; if a couple weeks before your cruise you’re notified that the itinerary may change, you’ll probably need to go with the flow and hope for the best. Calls to the cruise line beforehand generally won’t help, nor will complaining get you special treatment.

If you opt to cancel on your own within 30 days of sailing, you’ll forfeit your entire cruise fare (partial amounts if canceled further out). Travel insurance isn’t likely to cover you unless you purchased a “cancel for any reason” waiver.

Viking River Cruises, for example, offers a “cancel for any reason” waiver in its Travel Protection Plan that provides a combination of refund and vouchers for a Viking cruise to be taken within 12 months of issue. Conversely, its standard Service Guarantee—which gives guests who are dissatisfied with food, service, or shore excursions on board a chance to complain, and if the issue isn’t rectified in the next 24 hours, leave the ship with a full refund—doesn’t apply to Acts of God.

If you decide to go ahead with your amended itinerary, here’s what to expect

Cruise lines do have contingency plans designed to preserve as much of the original itinerary as possible—albeit often with less smooth sailing.

With two ships on the Elbe this past August, CroisiEurope was able to split the itinerary in half—with Elbe Princesse cruising on one side and Elbe Princesse II on the other; passengers switched ships at the low-water area, DaCosta said.

However, some cruisers on a Scenic itinerary from Budapest to Amsterdam (on the Danube and Rhine rivers) in August posted online that they had to change ships three times and take a ferry through the Rhine Gorge.

Katharine Bonner, Senior Vice President of Tauck River & Small Ship Cruising, reported that of the line’s 10 ships in Europe, just one was cancelled and a few others moderately affected, all on the Danube. The most common impact was that guests were moved to another Tauck riverboat on the far side of a low-water area, where they resumed their regular itinerary. In other cases, guests took buses to some areas for sightseeing and returned to overnight on a stationary riverboat.  

As a cruiser, you have rights—but it’s wise to be prepared up front

If your itinerary is significantly altered by water levels mid-cruise—what then?  Because you agreed to the cruise line’s terms of contact, unless your cruise is cancelled (upon which you should receive a full refund or vouchers for a future cruise) any conciliatory compensation is up to the discretion of the cruise line.

Tauck’s policy, for instance, is that refunds and/or travel vouchers will be determined on a departure-by-departure basis following the conclusion of a cruise, when the circumstances can be reviewed and evaluated. CroisiEurope’s policy notes that passengers will be compensated for any missed tours, on a sailing-by-sailing basis.

Your best bet: Ask about the cruise line’s water-level policy up front before booking, and if you’re concerned shell out for trip cancellation insurance with a “cancel for any reason” waiver. If you feel your cruise was negatively impacted by water levels, make your dissatisfaction known during the cruise, so the line is aware that you expect compensation for the inconveniences. Like the weather, compensation can’t be guaranteed, but cruise lines that value their passengers will likely try to offer some amends.