Lake Thoune in the Bernese Oberland holds nearly 4,600 tons of military munitions submerged at depths between 150 and 215 meters. This makes it the largest known military immersion site in Switzerland. The munitions, including shells, grenades, bombs, and cartridges, were placed in the lake between 1920 and 1963, with about a third dating back to World War II. The Federal Department of Defence (DDPS) has stated that recovering these items would pose more danger than leaving them undisturbed, as it could lead to explosions or release harmful substances trapped in the lakebed. A layer of silt, ranging from 25 centimeters to 2 meters thick depending on the location, has formed over the munitions. This silt acts as a natural barrier, helping to contain any potential hazards. Regular testing of the lake's water and sediments has not found any direct evidence of pollution from the submerged weapons. However, more than 40 percent of the lake's coregonids — a type of fish — show unexplained congenital and sexual abnormalities. Scientists have not yet linked these issues directly to the presence of the munitions. Switzerland's military has submerged more than 8,200 tons of munitions across several lakes, including those in Brienz, Uri, and Gersau. This practice was common between 1918 and 1964, when environmental regulations were less strict than they are today. A notable event in 1948, when an explosion damaged the Mitholz munitions depot, led to an increased amount of munitions being submerged in Lake Thoune to prevent their detonation on land. The armasuisse agency, responsible for managing Switzerland's military equipment, has launched an ideas competition to explore more environmentally friendly methods for extracting the munitions. However, both political and environmental experts currently agree that the safest and most responsible course of action is to leave the munitions in place, where they are considered to be securely contained.