Why's the water blueish?

I'm no expert on marine physics and light techniques and whatnot but I think I can give a small hand. I think its partly to do with light refraction and junk (like blue sky) and something to do with whats in the water. In the Rockies here, lots of ponds are a deep turqoise because of the copper inside them. I've seen a few red lakes in Arizona because of some iron in them. I've seen yellow water in a slew near a sulfur mining site becase of the dissolved sulfur. Could be something in the water, I suppose.