An explanation of why the sea appears blue.
Why is the sea blue?
Contrary to popular belief the colour of the sea is actually influenced by the wavelengths of colour which are absorbed by the water rather than the water itself. The orange, yellow and red wavelengths of light are absorbed by the liquid, whilst the shorter wavelength colours such as blue and purple are not, causing the water to appear to us as a shade of blue. The purity of seawater throughout the earth can of course vary significantly, this variation in its constituent make up can also cause variation in our perception of the colour of the water.
Sea water colour is also impacted significantly by the biology which live within it. Microscopic single celled algae utilise green chlorophyll pigments to capture energy for photosynthesis, reflecting green electromagnetic radiation, whilst absorbing radiation within the red and blue parts of the light spectrum. This causes the sea to appear much greener within areas of high prevalence.