Several sunken World War II-era Nazi warships have resurfaced in the Danube River amid a major heatwave and prolonged drought. The vessels became visible as the water level in Europe’s second-longest river fell to record lows.

Photos and videos posted on social media showed massive shipwrecks lying in the water and on a sand ridge in the middle of the waterway near the village of Prahovo in Serbia.

Elsewhere, the wreck of a Hungarian cargo ship that sank in 1937 resurfaced near the Croatian village of Opatovac.

Some 200 vessels could be lying on the bottom of the Danube River, according to the European Investment Bank. River transport has nearly come to a halt due to the low water levels, according to Hungary’s Transport Ministry.

Hungarian Prime Minister Peter Magyar also said that the Paks nuclear power plant, which covers nearly half of Hungary’s electricity needs, could be shut down for weeks because of insufficient water levels.

In Budapest, a German WWII artillery shell was found near Margaret Bridge – one of the city’s major traffic arteries – last week. The discovery prompted brief safety closures as a bomb disposal team was deployed to the area. Hungary’s national weather authority also reported a record-low water level of 23cm in the Danube as it flows through the city. The previous all-time low, set in 2018, was 33cm.

In northern Bulgaria, the drying-up river revealed what is believed to be the remains of a mammoth. The bones were found by a local resident of the village of Ryahovo. Nikolay Nenov, a director of a regional history museum in the nearby town of Ruse, called the discovery “very important for science.”

The Danube is expected to go even lower in the coming days, with no significant rain forecast and temperatures expected to exceed 38 degrees Celsius (100 degrees F) in the region, according to AP.