Did you know that some colours disappear the further you go underwater? You might have already noticed, the avid little snorkellers and divers you are, that the further you go underwater, the less colours your eyes seem to pick up. Everything just looks blue or green, and that’s not just cos ‘water is blue’, it’s because the other colours on the spectrum disappear. That’s right, they disappear.

Maybe we sound like a bunch of mad men – how can colours disappear?! It’s time for a fun little science lesson my friends, from the ‘real’ colour of water, to which colours disappear when, and what colours fish can see the best. You know, so they can all see you and come out to say hi, giving you awesome snaps for your GoPro.

Which colour disappears underwater first?

We’ve already posed the question so we’ll answer this one first. Basically, colours are wavelengths of light. Take this in as a fact, no need to process it or ask why. These wavelengths have different, well, lengths according to how much energy they carry. The visible light spectrum (colours you can see with your eyes) is ordered from least to highest energy: red, orange, yellow, green, blue, and violet. The colours lowest in energy are the first to be absorbed by water.

At what depths do the different colours disappear?

Going from the information above, red is the first colour to be absorbed by water as it’s the lowest in energy. Here’s a rough breakdown of which depth each colour will disappear:

  • Red – 4.5 metres,
  • Orange – 7.5 metres,
  • Yellow – 10.5 – 13.5 metres,
  • Green – 21 – 23 metres

By the way, this depth also takes into consideration horizontal distance. So if you’re 5 metres underwater and looking at a pretty piece of coral 5 metres away, then the light has actually travelled 10 metres, filtering out all reds! Go in for a closer look 😉

What is absorbing the light underwater?

Good question. Basically, water is about 800 times more dense than air. You may have noticed that it’s more difficult for your body to move underwater, and same goes for light. In water there are tonnes of microscopic particles that both reflect and absorb light.

When light hits those particles it is either scattered or absorbed, and the remaining light presents itself as whatever colour you’re seeing. The further light travels, the less colours are visible, with eventually no colours at all with all the light absorbed (in the deep, dark sea!) Of course, if you introduce white light via flash from your camera or a torch, then all the colours are made visible again.

What colour of light travels the farthest underwater?

Blue is the colour that travels the furthest underwater, hence why during those deep dives everything seems to be tinted blue. If you were to shine a light at those depths, you’d make visible all the other colors of the spectrum and illuminate a wonderful rainbow of colours.

If you’re looking to take some stunning underwater photography, it’s a good idea to keep all this information in mind – unless you do want to end up with a bunch of photos of blue corals.

What is the real colour of water?

You’ve always been told that water has no taste, smell, colour, or gender. But there’s a difference between perceived colour (colour as we see it) and actual colour (the real colour of an object). As we mentioned before, there are plenty of things that can affect the way we perceive colour, from the particles contained within it (like algae) to the depth at which we’re looking (due to light absorption). For that reason, water can appear all kinds of colours.

Maybe you’ve heard that the oceans appear blue because they’re reflecting the sky. While that might be valid to a certain extent, it’s also been revealed that water might in fact actually have a bluish tinge to it after all. While small amounts of water always appear clear, water can pick up a bluish tint as its density increases (piling on more and more of the bluish tint until it becomes visibly blue).

There’s a complicated explanation behind all this which might be a bit much for a humble little blog article, but we’ll give you a quick rundown. Basically, the absorbed light causes the water molecules to vibrate rapidly, and that’s what causes the blue tint. Apparently, water is the only known substance that gets its colours from vibrations rather than interaction of light and electrons. It’s also a necessary substance for all life. Crazy stuff, water is. That’s why we love being in it!

What colour do fish see the best?

Whether you’re looking to attract fish to take a great photo or to keep yourself hidden, you’ll hear different things from different people. Some say certain colours are picked up more easily by fish, others say it doesn’t matter. While snorkellers and divers are relatively chill on the matter, fishermen get into a heated debate over it.

There are all sorts of arguments online about which colour is best to use to lure fish to your line, but there seems to be one general consensus: nobody knows what a fish sees. We haven’t been able to get into the head of a fish just yet, and we already know that other animals can’t see certain colours. That said, you’re best off following the above information on underwater colour absorption if you want to get the attention of a fish while snorkelling. So since red is first to be absorbed, if you’re diving deep underwater then blue will be the easiest for fish to spot (assuming that their eyes work the same as ours do!)

The universe is a beautiful and tricky place, and there’s an incredible amount of information to be learned about everything. There are processes constantly at work, light being flung about and scattering and absorbing and reflecting, and that’s what allows us to witness the vast diverse beauty of the world around us!