thread was there yesterday
I don't think there's copper in them thar hills (scoff?) and a lot of high-altitude lochans have interesting algae, so I think it's just that

I've seen plenty of people swimming in it, and I'd imagine if it was bad there'd be some kind of signage as it's a popular spot, with people picnicking on the beach
permalink especially since it's so accessible
I love the Cairngorms.
permalink Afraid a detailed knowledge of copper mineralisation
of the Highlands is beyond my ken...

Although there is lots of bits and bobs of mineralisation all round the Caledonides. I'd be surprised if there was enough in groundwater to turn a lake green though. And Cu is usually only a minor component generally
permalink cheers fellas!