The Color of Water

Water is a great chameleon, seemingly able to change color in an instant, yet we seldom notice the changes even when we are gazing out to sea. We are so accustomed to seeing the many colors of water that we rarely take note of where these colors come from.

Clear water in Indonesia appears blue-green in shallows, dark blue in deep

So, what gives water its color? When we pour distilled water into a glass it appears clear and colorless. In fact, although it is almost transparent to visible light, it is very slightly blue.

Looking down into deep clear open ocean, the water appears blue, dark blue. (see my blog post on the Kuroshio current, Taiwan)

Open ocean water appears dark blue

That's because other wavelengths of light are more readily absorbed.  Red is absorbed first, and next orange and yellow too. Blue and green penetrate through shallower water and blue penetrates farthest.That’s why we commonly see a variety of greens and blues in shallower water, but only blue in deep ocean.

Closer to land, plankton (see article for plankton distribution) typically makes the water appear more green or brown.

Plankton colors this Pacific coastal water green

But that’s not the end of the story. China’s second largest river is aptly named “Yellow River” due to the color of the mineral sediment it carries to the sea, and that affects the sea color too over a considerable area near its mouth. Rivers commonly carry silt from runoff, especially when in flood, and this can color the water red, yellow, brown or grey depending on the eroding soil type. On the coast, waves stir up shore sediments that color the water.

A suspension of silt colors this French river yellow

Not all color is from particles in suspension. Dissolved tannin from vegetation can turn a river blood-red, orange or yellow. In a glass such river water is clear and the color of whisky, or black tea. It’s not cloudy. You cannot filter out dissolved tannin. The red color of tannin-rich water acts as a red filter, filtering out other colors of light including blue. But red light cannot penetrate far into water anyway. Deeper water appears black. Such tannin-rich streams are referred to as black water rivers.

Orange tannin-rich water flows across a track in Australia

The true color of water, very slightly blue, plus what is in it, dissolved or in suspension, still only accounts for part of what we see. Sometimes the surface is colored with a layer of yellow pollen, or with duckweed, so then it is the color of the surface covering we see. 

Duckweed colors this waterway green

At other times the water is clear and shallow, and we see the color of the sand or mud of the bottom.

Here in Florida we see the color of the bottom as the water color

And then there are reflections that blend with or completely hide the colors underneath. A blue sea under a blue sky can turn grey on an overcast day. The color we see is often the color of the sky But you can gaze out over blue water in one direction and turn your head to see the same water appear green with the reflection of a green hillside. Given the water surface is not always flat, those reflections can come from many directions, sending a mosaic of colors dancing across the surface.

Reflection of a red hull in Seattle borders sky blue

Artists have long made use of the crazy abstract patterns and color combinations light creates on water, 

Abstract patterns of reflection from a moored ship

and they also tackle the multiple worlds revealed when you glance down into the water to see first the reflections of above-water surroundings, then the surface meniscus with floating debris, and below, through the underwater scene to the dancing patterns of light cast by the lens of surface ripples onto the bottom.

We see colors of the bottom, the water and reflections

Water can appear in all the colors of the rainbow. I find it always rewarding to take time to identify where the colors are coming from.

All the colors of the rainbow

Find more about the Color of Water on Nigel Foster YouTube channel. Interested to have Nigel make a presentation to your group? Check out nigelkayaks