Science stuff you got wrong at school

Water IS blue, not just because of the sky

Many believe that lakes and oceans are blue "only" because they reflect the blue sky. Actually water looks blue because water is blue; the water molecules do absorb some light, and they absorb red frequencies more than blue. The effect is small, so the blue color only becomes obvious when observing layers of water many meters (or more) thick. (This effect is noticeable to a lesser amount in white-painted swimming pools.) In salt water or mineral-laden fresh water, the color of dissolved minerals can also be seen.

Sky-reflection does play a role, but only when the water surface is very calm, and only when the water is observed at a glancing angle less than approximately ten degrees.

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