According to The Guardian, some areas of the River Loire in Germany can now be crossed on foot, while the Rhine is becoming "impassable to barge traffic". The paper reports scientists are warning the drought could be "the worst in 500 years".

However, despite the threat of disruption, river cruise companies are reassuring clients they are monitoring the situation closely and amending itineraries accordingly.

Lucia Rowe, managing director of A-Rosa River Cruises, said it was "not uncommon" for water levels to fluctuate, stressing river cruise lines are adept at dealing with these situations. "When water levels become low, we monitor the situation on a daily basis and are in constant dialogue with the relevant port authorities and respective water management offices," she told TTG.

"If it becomes necessary, we adapt our itineraries and use our extensive experience in navigating Europe’s rivers to make suitable adjustments. River cruise lines are able to react to a change in situation and find suitable, attractive alternative ports.

"Furthermore, when amendments are made, we always arrange additional onboard activities such as extra culinary events and local musicians and we offer additional excursions as and when needed."

APT and Travelmarvel head of sales and business development Brad Bennetts said fluctuations in water level were something the business and wider river cruise industry "have always had to contingency plan for".

"We are lucky we have very loyal, understanding and sensible customers who appreciate these are situations beyond our control, and who have been appreciative of the fact that they can still take their well-deserved holidays, with almost all customers proceeding with their travel plans," he said.

Bennetts praised the brands’ agent partners, thanking them for their "professionalism and seamless communication". "While this extended period of elevated temperatures does mean we’re dealing with more low water than we would usually expect over the season, we are experienced in managing changing water levels.

"Our operations are set up so that we can quickly and seamlessly respond to any changes in external factors and continue delivering outstanding holiday experiences for our guests. As such, we haven’t had to adapt very much; instead, it’s been a case of working at pace and managing more volume. The team has risen to the challenges very well."

Jamie Loizou, managing director of AMAWaterways, told TTG all of the company’s river cruise vessels were still operating their itineraries as planned. "We are monitoring very closely the situation on certain sections of the Rhine and adapting our schedules as needed," he said.

"As the water levels on the rivers can change quickly depending on local rainfall, we have a dedicated communications team in place to alert our guests and valued travel agents if there are major modifications affecting their upcoming river cruises and assist with any changes that may be required."

Ellen Bettridge, president and chief executive of Uniworld, added that although the line may have to make changes to some itineraries – and has had to cancel "a few" voyages – impacted guests and travel partners have, and will, receive updates and the opportunity to rebook onto another sailing.

"The nature of rivers is that they ebb and flow with the seasons," she said. "We have made adjustments as necessary with current low water levels caused by the staggering summer heat."