Very clear water is dead-er than turbid water. Very clear water means nothing is living in it.

That depends on a lot of things. There are lots of clear mountain streams with all kinds of things living in them, and not all brown streams are brown for the same reason.

I've seen crystal clear lakes in the Alps teaming with life - aquatic and amphibious. But I don't think that's what my late grandfather meant.

I think he was talking about less turbid water than it is today. I don't think I could see my hand if I were to ever plunge it in the Seine, not that I'm foolish enough to try.