As Europe bakes this summer under record heat waves, droughts have also caused water levels to plunge on rivers and lakes across the continent.

In the Netherlands, the Waal River is so low that it has fallen below the bottom marker on bridges.

In Germany, the Rhine is so dry, it’s causing shipping problems.

And in Spain, receding waters in one reservoir have revealed a prehistoric treasure.

The Dolmen of Guadalperal, or Spanish Stonehenge, has been exposed in the province of Cáceres‎ for just the fourth time since the 1960s. The stones date back thousands of years but were flooded because of development under the dictatorship of Francisco Franco.

Elsewhere in Europe, so-called hunger stones — markers placed by people in droughts from years past — are appearing in rivers once more.

It’s not uncommon for water levels to drop in the summer months, but this year is especially extreme.

“It’s quite extraordinary, particularly for this time of year,” Martina Becker from the German company HGK Shipping told the BBC. “This is an unusual situation for us, and the question is what happens in October, when the usually dry months arrive. We are already approaching the record low level we had in 2018. We could reach that level next week.”

Weather disasters like droughts are inextricably linked to human-induced climate change. The planet has already warmed 2.1 degrees Fahrenheit since 1880, according to NASA, and that’s making disasters worse. Stopping this vicious circle will require drastically reducing our reliance on climate-polluting fossil fuels.