The water acts like a mirror reflecting the color of the sky, and the color of the sky is caused by the refraction of the color blue in the stratosphere and ozone layer. All other colors come through, thus making the sky appear blue, and the sun appear yellow, even though it is actually white.
Because the water reflects the color of the sky. If you are near a lake where there are lots of trees you might notice that the water is sorta green, that is because the water also reflects the green color of the trees. If the sky were.... Let's say purple, the sea would also look purple.
1 year ago
Last edited at 10:12PM on 4/5/2012
It is not because it is reflecting the sky but they are both blue for similar reasons. From scientificamerican.com: "The ocean looks blue because red, orange and yellow (long wavelength light) are absorbed more strongly by water than is blue (short wavelength light). So when white light from the sun enters the ocean, it is mostly the blue that gets returned. Same reason the sky is blue." In other words, the color of the ocean and the color of the sky are related but occur independently of each other: in both cases, the preferential absorption of long-wavelength (reddish) light gives rise to the blue."