Why is the sea blue ?

In the first place, the sky is blue because the molecules in the atmosphere scatrter the blue part of the spectrum, and the red and yellow parts of the spectrum tend to pass straight through. To us looking from the ground, the blue light seems to be coming from everywhere (this is called 'Rayleigh cattereing'); hence the sky seems blue.

The reason why the sea seems blue is similar; but a little more complicated. The sea does reflect the blue colour of the sky (or can appear grey in overcast weather), but this only applies to the surface of the sea. As well as reflecting the blue from the sky, the water molecules scatter the blue light in much the same way as the air molecules in the sky. This accounts for the 'natural faint blue colour'.

In addition, the water also absorbs more of the red and yellow wavelengths (which warm the sea), leaving the blue part of the spectrum, as well as part of the green. This is why deep water can appear bluish-green. (The absorption of the red wavelengths can be noticed by looking at a red object under deep water. It will appear black; because only blue light is reflected back to us.)

Eventually, at sufficient depth, even the blue light will have been absorbed or scattered away, and deep water will be black and lightless.

This scattering effect is even stronger if there are colloidal materials (very finely divided particles) in the water, such as finely divided clay particles. These can increase the scattering effect, turning the water an intense blue (which can sometimes be seen in flooded abandoned quarries). The scattering effect is also greater with ice; which results in the intense blue colour we see if we look down a crevasse in a glacier, or down a hole in the snow made by a ski stock..

For complete, scientific explanations of the scattering effect, look up 'blue sky' in Wikipedia.

The color of the surrounding sky reflects itself on the sea and gives it its color.

As to the deeper layers, the blue color is given by the penetrating sunbeams. When a sunbeam hits the water surface, it doesn’t stop its course at once, but splits into different hues as it goes deeper. The color yellow disappears along the first meters, then the red fades, and finally the green. The only color left is blue.

So, what gives the sea its different hues are its variations in depth. The shallower it is, the lighter the blue (we can even have green); the deeper it is, the darker the blue (it can even get black).

Now you may wonder why there’s a red sea and a black sea? Well, the other colors we can find in the sea are related to the nature of the bottom of the sea (corals, sand,…), or to the elements in suspension in the water (earth, weeds, pollution,…).

And it's green in California. And an amazing blue-green in the Caribbean.

Is it a combination of 1) the reflection of the color of the sky, 2) the amount of moisture in the air, 3) the teensy-weensy plant and animal life in the water, too small to make out with the naked eye, but causing an effect, nevertheless, 4) the temp. of the water and of the air? I'm not really sure, but that's my best guess. ;)

Lol Honey all can think of is the reflextion of the Sky,in Greece the water is also like bright Blue and it's beautifull.

Hope you had a nice time in Cape Verde.xxx

The sea is not really blue, it is really clear, the sea is just a reflection of the blue sky. On a storm, you won't see the ocean blue now would you?

It's because the sky is reflected into the sea, that's why it seems to be blue

Well it could be polution or coral or maybe just the sun reflecting to the sand which creates a blue colour. Or that the water was so clear that it was blue????

It is not blue, they sky is and reflects in the water. the sea around the coast of England is grey cos it is always bloody raining and grey skies.

reflection of the sky in sea water.

The water reflects the sky.