Thousands of tonnes of munitions dumped in Swiss lakes in the last century will not be recovered, the defence ministry announced on Tuesday.
A study ordered by the ministry in 2004 found that clearing them up would cause more harm to the environment than leaving them where they are.
Most of the items were dumped in the lakes of Thun and Brienz in the Bernese Oberland, and in two parts of Lake Lucerne.
Experts found that the munitions contained eight potentially harmful substances for the environment, including TNT, mercury and lead. But after examining the movement of water and sediment, they concluded that the munitions were unlikely to corrode.
They believe instead that the sediment will cover them, preventing contamination.
The only way to recover the munitions would be to use a dredge which would stir up the sediments on the lake bed and have a serious impact on the ecosystem. There could also be a risk of explosion during the course of handling.