Why the Ocean is Blue

There are several theories: 
•  Blue wavelengths are absorbed the least by the deep ocean water and are scattered
and reflected back to the observer’s eye
•  Particles in the water may help to reflect blue light
•  The ocean reflects the blue sky


Most of the time the ocean appears to be blue because this is the color our eyes see. But
the ocean can be many other colors depending upon particles in the water, the depth of
the water, and the amount of skylight.

The colors we see depend upon the reflection of the visible wavelengths of light to our
eyes. The Franklin Institute provides a good explanation of how we see color at
http://www.fi.edu/color/color.html.

Wavelengths of light pass through matter differently depending on the material’s
composition. Blue wavelengths are transmitted to greater depths of the ocean, while red
wavelengths are absorbed quickly. Water molecules scatter blue wavelengths by
absorbing the light waves, and then rapidly re-emitting the light waves in different
directions. That is why there are mostly blue wavelengths that are reflected back to our
eyes.

Sometimes oceans look green. This maybe because there of an abundance of plant life or
sediment from rivers that flow into the ocean. The blue light is absorbed more and the
yellow pigments from plants mix with the blue light waves to produce the color green.
Sometimes parts of the oceans will look milky brown after a storm passes. This is
because winds and currents associated with the storm churn up sand and sediment from
the rivers that lead into the oceans.

The ocean may also reflect the blue sky. However this is prominent only at relatively low angles and when the water is smooth.

From Everyday Mysteries