That's good to know, so the extra vividness of Blautopf's water is caused by the carbon particles. That must be the reason why some lakes are bluer while some have lighter blue color.
My first thought is because of some form of algae or bacteria, like the case of some thermal lakes. But the case of Blautopf seemed different with the one that I searched, so I went for the reason that mention earlier. Water's reaction to light :) Thanks a lot man, for the added info. Once again, I learned something new :)