Europe’s drought-stricken Danube has fallen to historic lows, exposing wrecks from Nazi Germany’s Second World War fleet while also threatening power generation across central and eastern Europe.

The same lack of water that has uncovered decades-old weapons and unexploded bombs is now constraining the river systems needed to cool nuclear reactors and generate hydroelectricity.

The most visible remnants have emerged near Prahovo, on the Serbian side of the Danube close to the Romanian border.

Dozens of German military vessels have reappeared on sandbanks and in the shallow riverbed, their hulls partly exposed after years beneath the water.

Some are believed still to contain weapons and explosives, making the area hazardous for both navigation and any future removal work.

The ships were part of Nazi Germany’s Black Sea fleet and were deliberately scuttled in September 1944 as German forces withdrew and tried to slow the Soviet advance.

Historians estimate that as many as 200 vessels were sunk in the Danube during that retreat.

The wrecks have surfaced during previous droughts, but many remain in place because of the danger posed by unexploded munitions.

Other relics are emerging along the river's course.

A German military motorcycle was recovered in Budapest after the Danube gauge there fell to 10 centimetres, below the previous record low of 33 centimetres set in 2018. In Slovakia, authorities safely removed and later destroyed an unexploded British bomb weighing about 700 kilograms, another legacy of wartime attempts to disrupt German transport along the river.

The low water is the product of prolonged drought and repeated heatwaves across the region.

Slovakia recorded a national temperature high of 42 degrees Celsius at Dolné Plachtince, while rainfall deficits and sustained heat have driven rivers, reservoirs and groundwater lower across much of Europe.

The Danube, which runs through or along the borders of 10 countries, has become a measure of the wider climate and water emergency.

For governments, the more immediate concern is energy.

Hungary's Paks nuclear power plant, which relies on the Danube for cooling water, has drastically reduced output as the river reached unprecedented levels.

The four-reactor plant normally has capacity of about 2,000 megawatts and supplies close to half of Hungary's electricity.

Its output has fallen to roughly 240 megawatts, and officials have warned that a full shutdown may be necessary if water levels continue to decline.

Hungary has urged large industrial users and households to conserve electricity, while relying more heavily on domestic generation, renewable power and imports to keep the grid supplied.

The reductions at Paks are a safety measure, not a nuclear accident: without enough water to cool the reactors and manage the temperature of discharged water, plant operators must cut output or take units offline.

Romania has faced a similar problem at its Cernavodă nuclear plant.

One reactor was shut down in a controlled, preventive operation because the low Danube flow threatened cooling equipment.

Authorities have used emergency engineering measures, including a controlled blast to remove a rock obstructing water flow and the sinking of loaded barges to redirect water towards the remaining reactor.

The drought has also curtailed hydropower in Serbia and added pressure to electricity systems across the region.

River traffic is being restricted by shallow channels and the exposed wrecks, while power operators are preparing for continued heat and limited rainfall.

The Danube’s depleted flow is now affecting transport, historical safety and energy security at the same time.