I thought it might be the reflection from the sky but if that was the case, why does the ocean appears more blue the deeper you go?
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Open the graphic editing program of your choice, fill an area with a rich blue and set the layer’s opacity to 5%. Now duplicate that layer again and again. In my test a stack of 64 appeared the same as one layer with 96% opacity.
Eyadams is not fully correct.
Same reason the sky is blue, dude. Anything clear will look blue if you have enough of it.
Also, for an ELI25, check out Beer’s Law.
https://en.m.wikipedia.org/wiki/Beer%E2%80%93Lambert_law
A = εLc
For water, the absorptivity (ε) is low, but in the ocean, the path length (L) is huge, so the overall absorbance (A) is large enough for the blue color to become visible.
An easy to see example is how glass coffee tables are clear but often have green or blue sides. The glass has a slight color and looking through the pane from the side is the thickest part.
This is the absorption spectrum of water.
https://www.researchgate.net/profile/Hrebesh-Molly-Subhash/publication/258384344/figure/fig23/AS:325110046183441@1454523683523/Water-absorption-spectrum-The-original-data-consult-from.png
Note that the absorption is higher in the red than in the blue. This means that the light remaining after passing through water will have more blue left in it than red in lt. And will thus appear blue.
You can cut a tomato thin enough that the slices are barely red, more like pink and clear. But the thing as a whole is still red.
The reflection of the sky IS part of it. Even brown muddy water will look blue at certain angles because of this, and you can actually see the real color of the water if you wear polarized sunglasses (which can filter out life reflected off the surface). Water IS just a bit reflective
But also, as others have said, water does just also happen to be very slightly blue, the same way tinted glass can be green or brown. It’s just pretty faint and not obvious until it’s a LOT of water
What is in the water is what makes it that color.
Northern California oceans look green to me. Lots of nutrients. Algae. Zoo plankton.
Clear tropical water has almost no nutrients..
A pond that is clear blue has no life to it, however if it is completely covered/ darkened same may apply. Excluding salt water reefs…
You know how when light passes through colored glass, the light that passes through is now that color? What’s going on is that all the *other* colors/frequencies of visible light are being absorbed by the glass, or being re-released as that color. For colored glass, this effect is pretty dramatic- stained glass has strong colors because the metals injected into the glass are *really good* at absorbing light of specific colors.
*All substances* that light passes through do this. There is no substance that is *perfectly clear*. But there are substances that aren’t very dense, or just absorb *very little* light. Our atmosphere is the former, and water is the later. Both take light traveling a pretty significant distance for our eyes to see their effects on light- and, as it turns out, both make that light tend towards the color blue.
Water absorbs Red light the most easily, then greens, and blue last. People see this effect the most strongly when scubadiving, because you can see the colors bleed out of the world as you go deeper and deeper, until barely any light at all is getting to that depth (not that you should be scuba diving to those depths, but you can definitely see the color red grow faint at reasonable diving depths).
So when you look at water in a clear glass, or water spraying out of a hose, those *look clear* because there just isn’t enough water for them to absorb a noticeable portion of the light passing through them, though they can definitely refract that light into rainbows and such.
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