CBSE Class 10 Answered

Lakes and oceans appear blue because the surface of the water reflects the color of the sky. The other reason is some constituents of sea water contribute to the blue colour of the ocean. Scattering from suspended particles also plays an important role in the color of lakes and oceans. Without scattering, all bodies of water would appear black.

One more reason is that most lakes and oceans contain suspended living matter and mineral particles known as coloured dissolved organic matter due to which light from above is reflected upwards and the scattered light appears blue.

In extremely pure water as found in mountain lakes, where scattering from organic particles is missing, the scattering from water molecules themselves also contributes a blue color.

Another phenomenon that occurs is Rayleigh scattering in the atmosphere. The horizon is about 4-5 km far from the line of sight and the air is densest just above sea level in the case of the ocean. This mechanism would add a blue tinge to any distant object because blue light would be scattered into one's line of sight.

Fountains and rivers are water bodies in which water is in rapid and random motion. This scatters the light in all possible directions and hence the water appears white or colourless.