The Nazi shipwrecks emerging from the DanubeAs water levels fall, travellers are getting a rare glimpse of history usually hidden beneath Europe's great river.

In practice, the Nazi shipwrecks emerging from the Danube.

Key points

• This August, receding water has additionally exposed a German army Wehrmacht motorcycle in Budapest and a 1, 543lb British bomb near Virt, Slovakia.
• Woolly mammoth remains – Ruse, Bulgaria: Bones exposed near the village of Ryahovo in July have been recovered by specialists from the Regional History Museum in Ruse.
• Nazi shipwrecks – Prahovo, Serbia: At least 20 wrecks have been visible from the riverbank at Prahovo, near the Serbian-Romanian border, this summer.
• "For archaeologists, these moments are extremely valuable, " Pavel Popov of the Regional Historical Museum in Pleven informed Reuters.
• This month, record-low water levels on the Danube have exposed at least 20 German warships near Prahovo in eastern Serbia.

As the Danube shrinks under extreme heat, the river is revealing a startling remnant of Europe's wartime past.

This month, record-low water levels on the Danube have exposed at least 20 German warships near Prahovo in eastern Serbia. Rusted hulls and broken masts are emerging from the river – the remains of a Nazi Black Sea fleet deliberately scuttled during World War Two.

Wrecks have surfaced during previous droughts, but this summer's extreme heat and drought have brought dozens of vessels back into view. Some are believed to contain weapons and explosives, turning this stretch of one of Europe's great cruising rivers into an eerie, visible battlefield.

For travellers cruising along the Danube this summer, the falling water is revealing a landscape – and history – normally hidden beneath the river.

Notably, the story of how they obtained there begins more than eight decades ago. By 1944, German forces were retreating on the Eastern Front as the Soviets advanced through the region, leaving a fleet of around 200 Nazi Black Sea vessels stranded in what was an area rapidly falling under Soviet control.

Meanwhile, the Danube offered an escape route, but the Iron Gates – a narrow and historically treacherous stretch of the river – created a bottleneck. In September 1944, German Rear Admiral Paul-Willy Zieb ordered more than 200 vessels scuttled as the Red Army closed in. The ships were deliberately sunk to prevent their capture and obstruct the Soviet advance.

Today, you can sit on the deck of a river cruise ship with a glass of wine and watch these beautiful countries pass by, but this same landscape has witnessed war, fascism, oppression and tremendous human suffering – Kenneth Reece.

Most have remained submerged beneath the river ever since, partly since numerous still contain unexploded ordnance and pose a hazard to navigation. Serbia has introduced an estimated €30m removal programme to remove some of the vessels, but progress has been slow as clearing the riverbed safely is complex.

For travellers, it's a striking sight along Europe's second-longest river. It stretches roughly 2, 850km (1, 770 miles) throughout 10 countries and centuries full of falling empires and shifting allegiances.

Kenneth Reece, a travel planner who lately cruised the lower Danube aboard the Avalon Passion, states reminders of the region's turbulent history surrounded them throughout their trip.

"We visited medieval fortresses, heard stories about life under communism and dictatorship, learned about the wars that have shaped this region and travelled through places where some of that history is still within living memory, " Reece remarked. "Hearing regarding the WWII-era German shipwrecks beneath the Danube went on another layer. The history wasn't only in museums or monuments. Some of it was quite literally beneath us." How to see what the Danube has made public.

Nazi shipwrecks – Prahovo, Serbia: At least 20 wrecks have been visible from the riverbank at Prahovo, near the Serbian-Romanian border, this summer. Some are still believed to contain weapons or explosives, so they should be viewed from the bank rather than approached. Visibility will change as river levels rise and fall.

Woolly mammoth remains – Ruse, Bulgaria: Bones exposed near the village of Ryahovo in July have been recovered by specialists from the Regional History Museum in Ruse. After conservation and study, they're projected to go on display at the museum, concerning 30km from where they were discovered. What else the river is revealing.

In practice, the Nazi ships aren't the only remnants emerging as the Danube falls.

This August, receding water has additionally exposed a German army Wehrmacht motorcycle in Budapest and a 1, 543lb British bomb near Virt, Slovakia. It was afterwards safely detonated. While near Ryahovo, archaeologists unearthed woolly mammoth tusks and bones dating back thousands of years, at Gigen in Bulgaria, falling water has made public the remains of the ancient Constantine Bridge.

"For archaeologists, these moments are extremely valuable, " Pavel Popov of the Regional Historical Museum in Pleven informed Reuters. "It gives us a rare opportunity to observe, document and study it in its real environment."

Droughts and fluctuating water levels are not new to the Danube. Europe is the fastest-warming continent, according to the EU's Copernicus Climate Change Service, warming at more than twice the global average. Rising temperatures are intensifying heat extremes and altering rainfall patterns, contributing to repeated low-water events that disrupt navigation along the river.

"The Danube was revealing warnings from our past while, at the same time, perhaps giving us a warning about our future, " Reece remarked. What low water means for travellers.

For context, the consequences are already being felt by visitors to the region. This summer's low waters have forced Danube cruise operators to cancel sailings, change itineraries, transfer passengers between ships and employ coaches to bypass unnavigable sections of the river.

In short, the Nazi shipwrecks emerging from the DanubeAs water levels fall, travellers are is the central thread here, and readers can expect follow-up reporting as the picture becomes clearer.