The fact that there are ammunitions at the bottom of the lake may be true, but whether it is affecting the local wildlife is probably far more debatable. What isn't debatable is that The Independent made a glaring mistake in the very first sentence of the article:

I was surprised by this, so I checked my map. According to that, the lake is 215 metres deep at its lowest point. There are several lakes in Switzerland that are deeper than this, including Lake Brienz, which is right next door and is listed as being 260 metres deep, and Lake Geneva is over 300 metres deep. There are probably others, too.

If they can't get basic facts like this correct then I'm not sure that the rest of the story should be trusted at all.