FAULENSEE, Switzerland  Kurt Klopfenstein has been fishing the waters off this Alpine village for over 30 years, but the object he dug out of his nets not long ago, in among the whitefish, perch, trout and pike, was like nothing he had ever pulled out before. A hand grenade, slimy to the touch but easily recognizable. “I gingerly tossed it back overboard,” he said, setting his nets from his rocking rowboat one recent evening.

It is a wonder a catch like Mr. Klopfenstein’s does not happen more often around here. For in the decades following World War II, the Swiss dumped more than 9,000 tons of munitions into the deep waters of Lake Thun, which stretch out placidly from this village.

Neutral Switzerland stockpiled the munitions  artillery shells, hand grenades, ordinary bullets and other ordnance  during the war in the event of an invasion by Nazi Germany or Fascist Italy, which never came about. Some caches included matériel seized from trains crossing from Germany into Italy in violation of neutrality agreements.

In the years up to 1964 the munitions were disposed of by simply dumping them into at least four Alpine lakes, with Lake Thun, an 11-mile-long body of water that is 700 feet deep in places, getting by far the lion’s share, at least 9,020 tons.