In essence, we are diving in the part of the crack that opens up between America and Europe as the continents drifts apart. The cracks and adjoining lake are filled by meltwater from glaciers some distance away, which passes through the porous underground and gets further micro-filtrated in the process.

Apparently, there is nothing left in the water, but water. There is an almost magical blue hue over the scenery that could be taken out of science fiction movie. It looks like we are on some foreign moon. In our drysuits, our similarity with astronauts is not too far off either.