What Color is Water?

»The blueness of the oceans can be seen from space. This is a time-lapse video from the Galileo spacecraft’s close pass of the Earth in 1990.

That cool, refreshing glass of water on a hot day may appear colorless, but water is actually a faint blue color. The blue color becomes visible when we look down into, or through, a large volume of water.
We see water in a variety of ways. It may be colored by particles, the presence of bacteria, or by reflecting the world above its surface. Ice and snow may reveal a vivid internal blue. Water itself has an intrinsic blue color that is a result of its molecular structure and its behavior.

Rivers and streams

There are other factors that can affect our perception of the color of water. For example, particles in water can absorb light, scatter light, and reflect light. Light may be absorbed by particles and solutes, as evidenced by the darker color of tea or coffee. Green algae in rivers and streams often lends a blue-green color to the water. Some mountain lakes and streams that contain finely ground rock, such as glacial flour, are turquoise. The surface of water can also reflect skylight.

Marble Canyon viewed from the Navajo Bridge over the Colorado River. The green color of the Colorado River is caused by the algae bloom in the spring snowmelt, while the Red Sea may get its name from the occasional bloom of red Trichodesmium erythraeum algae

Particles in water can scatter light. The Colorado River is often a muddy red color because of suspended reddish silt in the water.

Large bodies of water

It is often easier to appreciate water’s intrinsic blue when looking at large bodies of water, such as lakes, seas and oceans, when we are able to observe how sunlight changes color as it travels through a significant depth of water. When circumstances eliminate the reflection of blue skylight, it may be possible to observe that water is not entirely colorless.

Banff National Park’s Moraine Lake is turquoise because finely ground rock is present. We are able to observe the blue light produced by the water’s absorption, because light is scattered by suspended matter and so returns to the surface. Such scattering can also shift the spectrum of the emerging photons toward the green, a color often seen in water laden with suspended particles.	The surface of seas and lakes often reflect blue skylight, making them appear bluer. The relative contribution of reflected skylight and the light scattered back from the depths depends strongly on the observation angle. In this view of Crater Lake (Oregon, USA), the far side of the lake reflects the sky more, and the near side shows mostly the actual water.
The blueness of water is very apparent when diving. As one goes deeper, lower energy wavelengths penetrate the water less, eventually leaving only blue light from the higher energy end of the spectrum. Even when using an artificial light source, such as a flash, the objects close to the observer appear as their real color, whereas the objects further away appear to be blue.