As record-high temperatures have sent water levels plunging in Germany this summer, World War II munitions have surfaced. So far, 22 grenades, mines or other explosives have been recovered from the Elbe River in the German states of Saxony-Anhalt and Saxony.

Authorities warn that the public shouldn’t touch any they find. Instead, people should call the police to safely remove them, or in some cases, safely detonate them on-site. At the end of July, authorities detonated two anti-tank mines on the Elbe.

During the war, Allied forces dropped over a million tons of bombs on Germany. As many as 10 percent of these didn’t explode, according to Smithsonian. Every year, Germany discovers more than 2,000 tons of unexploded munitions that have been sitting in the ground for decades.

It’s such a problem that no company in Germany can start a construction project without first examining the ground for bombs. These construction searches commonly discover bombs, leading to mass evacuations.

Russian and American troops meeting along the Elbe river on April 27, 1945 in front of a bridge destroyed during World War II. Now, what is usually only seen below the waters surface is visible due to the drought. (Credit: Keystone/Getty Images)

In August 2017, Frankfurt ordered 70,000 residents to leave their homes—one of the largest German evacuations since WWII—while a bomb squad defused a 4,000-pound “blockbuster” bomb found near a construction site. This past April, authorities evacuated 26,000 people from the small German city of Paderborn to defuse a 1.8 ton-bomb also discovered during construction.

The Elbe River bombs aren’t the first instance in which lower water levels have revealed WWII munitions. In 2011, a drought revealed another 1.8-ton bomb along in the Rhine River. In that case, 45,000 people had to evacuate while a bomb squad dealt with it.

The lower water levels in the Elbe coincide with an intense heat wave that scientists say is made more likely with climate change. July 2018 was Germany’s hottest month ever recorded, reports Deutsche Welle, Germany’s international broadcaster. Temperatures in Bernburg, Saxony-Anhalt reached 103.1 degrees Fahrenheit. In the past week, water levels plunged to 20 inches in Saxony-Anhalt’s capital of Magdeburg, about an inch above the historical low in 1934.