The ships were among hundreds scuttled along the Danube by Nazi Germany’s Black Sea Fleet in 1944 as they retreated from advancing Soviet forces and still impede river traffic during low water .

However, this year’s drought – made worse by human-induced global warming – exposed more than 20 carcasses on a stretch of the Danube near Prahovo in eastern Serbia, many of which still contain metric tons of ammunition and explosives and constitute a hazard to navigation.

“The German flotilla has left behind a great ecological disaster that threatens us, the people of Prahovo,” said Velimir Trajilovic, 74, a retiree from Prahovo who has written a book about German ships.

Workers in the local fishing industry are also at risk, especially from Romania, which is just across the river.

Months of drought and record temperatures have hampered river traffic on vital arteries in other parts of Europe, including Germany, Italy and France. In Serbia, authorities have resorted to dredging to keep the Danube shipping lanes open.

By Prahovo, some of the carcasses reduced the navigable section on this stretch of the Danube to just 100 meters (330 ft) from 180 meters.

Scattered across the river bed, some ships still have turrets, command bridges, broken masts and twisted hulls, while others are mostly submerged under sandbanks.

In March, the Serbian government launched a tender for the salvage of carcasses and the removal of ammunition and explosives. The cost of the operation was estimated at 29 million euros ($30 million).