Colors of Water at Earth's Surface - Lakes, Rivers, Glaciers

Water molecules absorb long wavelength red light and scatter short wavelength blue light (Rayleigh scattering). This is why clear bodies of water appear blue. About two-thirds of Earth is covered by water with over 95% as oceans.

In clear, sunny conditions, clean lakes appear luminous and deep blue. The water is virtually pure and water molecules scatter blue light efficiently. Lakes will be a duller colour after rain or in cloudy conditions.

Lakes in heavily vegetated areas with high rainfall can appear brown or nearly black. The colour is from the breakdown of chlorophyll plant pigment in decaying vegetation and iron compounds in soil.

Glacier lakes appear green or blue but are always opaque because of suspended silt. The suspended silt at the surface reflect blue light from the sky.

Blooms of microscopic algae can result in green or pink lakes, particularly in farming areas which have fertiliser and animal waste run-off which contain nutrients such as phosphorus and nitrogen.

Sky colours can be reflected to an observer standing on the same level as the body of water, particularly if the water is clear and calm. An observer looking straight down on clear, shallow water can see through to objects below.

When looking down onto a coral reef, the reef looks lighter because of reflection of sunlight from coral in shallower water.

When underwater, water looks blue because most of the red light has been absorbed by water and only the blue wavelengths are scattered. Dissolved salts are transparent and make no difference to light scattering.

Deep below the surface of a clear blue ocean, all red wavelengths from sunlight will be absorbed. Red animals will appear black and other animals will appear bluer. A flash is needed to photograph true colours. At greater depths, virtually no light penetrates and everything will appear black.

The colour of coastal waters depend on the weather conditions like sunshine and wind. Clear, calm ocean water in sunny conditions only reflects about 3% of sunlight. White light enters the water and the blue light is scattered, making the water appear luminous blue.

Nearer the coast, water can look green, brown or yellow because of suspended particles like sand scattering light and reducing visibility in water. Suspended particles in the water are larger than water molecules and absorb blue light and scatter yellow and red light.

Microscopic algae and plankton can make the surface of coastal waters appear yellow, red, brown, blue-green or yellow-green. Muddy sediments can make water look brown. When green plant pigments break down, they can make coastal waters look yellow-brown.

Moving water, such as breaking waves look white, because of scattering of all wavelengths of light, which recombine to form white light. With large waves, some light may transmit though the wave. A shadow will result where the wave obstructs light.

The colour of rocks or sand only have influence in very shallow water.

Snow is ice-crystals with air-spaces between them. Clean snow is white because light is reflected and refracted in all directions by which recombine to form white light. Shadows appear blue because yellow light is obstructed and the only light reaching shadows is scattered blue light from the sky.

Glaciers appear bluish on a sunny day because of reflection of scattered blue light from the sky.

Ice in lakes often appears bluish, because of blue light from the sky. This is accentuated because there is little run-off and algae growth at this time of year.

When the sun is low in the horizon, yellow and red wavelengths of sunlight reflect off snow, resulting in other colours, such as yellow and violet.

Wetlands can look colourful, because some still water reflects light from the sky, and some parts are transparent showing plant foliage.

One can see the colour of boulders/pebbles through water of clear-water streams and creeks. Regions of fast-flowing water appear white from light scattering in all directions.

Hot springs can be vivid colours because of microscopic hotwater bacteria and algae.

Shallow rock pools show the colours of the plants and animals that are in them. Dissolved sea salt has no influence on the colours.

Rivers after rainfall can appear muddy brown, particularly in areas with iron-rich soil or clay.

Rivers can appear milky if they carry fine sediment. A rapidly flowing glacial river appears milky white. The river becomes bluer as the water slows down and the finer silt particles at the surface reflect blue light from the sky.

Some rivers are called black-water rivers because of the large amount of organic matter from decaying plant matter that absorbs all wavelengths of light. This occurs in areas of high vegetation such as jungles.

Clear-water rivers have little dissolved sediment. These rivers are transparent and have little run-off from eroded rock silt and organic matter.