The apparently pristine Gerardmer lake in the Vosges mountains of eastern France conceals a bleak legacy of 20th-century conflict -- dozens of tonnes of unexploded ordnance from the two world wars, reports FRANCE 24.
The lake 660 metres (2,170 feet) above sea level is a popular summer bathing spot and is sometimes also tapped for drinking water for the picturesque local town.
Gerardmer's mayor Stessy Speissmann-Mozas started asking questions about the water safety after the Odysseus 3.1 environmental group said samples taken from the lake showed high levels of TNT explosive, as well as metals like iron, titanium and lead.
The group said it found artillery shells in the mud at the bottom of the lake. Some were "gutted, allowing the explosive they contained to escape", Odysseus 3.1's founder Lionel Rard said in a documentary broadcast by the France 5 channel in May.
Samples sent to a German lab showed TNT levels among "the highest ever measured by that team", as well as metal concentrations above legal limits.
The mayor has said the government should pay for a more detailled study of the risks from the munitions that were initially dumped in Gerardmer by the French army. As a theatre of multiple conflicts over the past century and more, France is particularly afflicted by unexploded ordnance.
Most dates back to the world wars but shells are still found from the Franco-Prussian war of 1870, noted Charlotte Nihart of Robin des Bois (Robin Hood), an association that has charted unexploded bombs across France.
Unexploded ordnance is involved in around 10 deaths nationwide every year.
During the wars, retreating armies would dump munitions in lakes to stop enemy forces getting them, Nihart said.
In Gerardmer, disposal drives started in 1977 after a man was burned by a phosphorous shell. They continued through to 1994, removing explosives up to 10 metres below the lake surface.
"They took out 120 tonnes of munitions, made up of almost 100,000 individual pieces of different types from 1914-18 and 1939-45," said Pierre Imbert, an assistant to the mayor and former local fire chief and diver.