Just today I was chatting with one of my employers and ended up talking about the last time I flew over the Andes; I told him how there where lakes in some valleys that were of an intense turquoise colour; I suggested that the cause may be high copper content in the water. Could this be so?
Executive summary: water absorbs a small amount of light in the red region of the spectrum, making it appear pale blue (the complimentary colour.) We don’t notice this in a small glass of water, because there’s not enough water for it to work. There’s a picture of a long column of water in my first link, though, which shows a definite blue color.