Why Does the Ocean Look Blue?
The ocean usually appears to be blue. However, sea water, as anyone knows who has splashed about in the surf, is actually colorless. The blue appearance of the ocean is caused by sunlight. Sunlight is made up of all the colors of the rainbow: red, orange, yellow, green, blue, and violet.
When sunlight falls onto the ocean, especially where the water is deep and clear, only the blue color is reflected back to our eyes. Therefore, the water looks blue to us. Deep lakes and rivers look blue for the same reason.
In deep water, much of the sunlight is scattered by the oxygen in the water, and this scatters more of the blue light. Water absorbs more of the red light in sunlight; the water also enhances the scattering of blue light.
Some of the sunlight penetrates the water and is scattered by ripples and particles in the water (this tinges the appearance of the ocean with the color of the particles). Along the seacoast, the presence of dissolved matter and tiny sea plants and animals lends the ocean such colors as greens and browns.