Why is Water Blue?
As white light travels through water it is not only refracted and scattered, it is absorbed or 'attenuated' by the water. Varying wavelengths, or colours, are absorbed at differing depths; organic matter also adding to this absoption.
By one metre below the surface, sixty percent of light will be absorbed and by ten metres eighty-five percent. The first colours to be attenuated are red, yellow and orange, which is why when one is submerged, the topography looks blue or green. In natural light, marine life that is red will appear blue at depth and only by using artificial light will the true colours be revealed.
The attached underwater image is of a sea-pool and was taken today around 2pm. The rays of light are visible as they penetrate the surface of the water; the pool however remains orange in appearance, this is due to the fact that the depth was only a quarter of a metre.
