Why Tropical Waters are So Damned Blue

Petit St. Vincent

The shorter and darker the days in the Northeast, the greater the lure of warm white sand beaches fringed with palm trees and topped with bright blue skies. Should you heed this call and book passage to the tropics, try to remember that you’re supposed to turn your brain off and not question much beyond the timing of your next fruity frosty cocktail. I’ve never been too good at this, and so when I visited Petit St. Vincent in the Grenadines in January of this past year and obligingly tried to render myself slack jawed in my beach chair, I found myself both hypnotized by the color of the water and unable to stop wondering why, exactly, this water was so damned blue.

If such thoughts also pester you like so many sand flies (which were not a problem on P.S.V, by the way), a book called Color and Light in Nature will be of help. A single drop of water is crystal clear, a bathtub full has a slight blue tinge and the amount of water deep enough for an ocean is very blue indeed. To understand why, you need to remember that a single beam of light is white, but a prism will reveal that that beam contains all the colors of the rainbow. Water is a substance that does a good job of absorbing every color’s light but blue,  which it scatters.  The more water you’ve got, the bluer it looks.

There are some factors that boost the appearance of blue: surface reflection of the sky, for instance, and the color of the ocean bottom  — if it’s white it will also tend to reflect the sky and amplify the blue of the water. And there are other factors that diminish blue: a gray sky, for instance, or the presence of other things in the water  which absorb or scatter other colors, like algae, phosphorus,  stirred-up sand and so on.

So to have a really blue sea, what you need is depth, reflection and clarity. The same qualities, come to think of it, that you’ll also hope to find in your own mind as you remember how to relax and enjoy the warm ocean breeze.

About The Author


  1. Panama Hotel Reply
  2. Alison Wellner Reply
    • Tim Dinsmore Reply
  3. andrews Reply
  4. Irwin Reply