A sunken Nazi warship has resurfaced in the river Danube following low water levels in the record-breaking European heatwave.

The Danube River, which runs through 10 countries from southwestern Germany to the Black Sea, has receded to never-before-seen lows along much of its course, exposing rocks, sand bars and old shipwrecks that have rarely been seen before.

One German warship from World War II was exposed on the riverbed of the Danube in Prahovo, Serbia, as locals swam nearby to cool off in the heatwave.

European Investment Bank says it is among 200 vessels that lie at the bottom of the waterway, including destroyed cargo ships, tugs and barges. Elsewhere in the river, the wreck from 1937 of the Hungarian cargo ship Fulton has resurfaced near Opatovac, Croatia.

A renewed heat wave is bearing down on Western Europe and a prolonged drought half a continent away is setting record low water levels on one of Europe’s largest rivers, disrupting tourism and industry across the region.

In Budapest, Hungary’s capital, the national water authority measured the Danube’s water level at 23 centimeters (9 inches) on Wednesday morning, well below the previous all-time low of 33 centimeters (13 inches) set in 2018.

The low water level has forced popular cruise ships, where passengers usually disembark for sightseeing in Budapest, to dock far upriver, while cargo ships have stopped operating nearly entirely, according to Hungary’s Ministry of Transport and Investment.

Hungary’s Paks nuclear power plant, which generates nearly half the country’s electricity, could be shut for weeks, the prime minister said on Friday, while Romania declared a state of emergency as low water levels on the Danube cut power output.

Both countries face increasing their reliance on power imports during a heatwave that is expected to boost demand for electricity.

In Hungary, peak evening electricity demand is expected to rise by 20%, prompting the government to ask major industrial users to curb consumption.

Romania’s Prime Minister Ilie Bolojan said the country would seek to import more electricity from Ukraine, Greece and Bulgaria.

“I have declared a state of alert on a national level throughout August as a result of the drop in electricity production because of drought and low river volumes, especially the Danube,” Bolojan said.

“Both (Romania and Hungary) have cut our nuclear power production in half.”

Romanian nuclear power producer Nuclearelectrica ROSNN.BX has shut down one of its reactors.

Paks’ four Russian-made reactors are operating at less than 50% of their combined 2 gigawatts capacity and are expected to be shut down completely on Tuesday or Wednesday for the first time in 44 years as water levels are forecast to fall further.

Water from the Danube is used to cool the facility.

The reactors can be restarted once water levels recover sufficiently for safe operation, “but this is not expected to happen in the next weeks,” Hungarian Prime Minister Peter Magyar said during a briefing at energy company MOL’s Danube refinery in Szazhalombatta.

Magyar said on Thursday that Hungary could meet its energy needs through imports. However, the combination of lower domestic generation and higher demand could create a critical situation for the power system.