Water normally does not have a color. When we drink a glass of water, take a shower or bath or get caught in the rain, we don’t expect to be drenched in blue. And yet we are also used to the oceans and seas coming in a wide range of blues. Why is there such a difference? Exactly why is the ocean blue?
A lot of people might think that the oceans and seas are blue because they are reflecting the blue of the sky. This is not entirely accurate. It is actually sunlight, and the way it is dispersed, that causes the ocean to appear blue to our eyes.
Light is made up of different colors with varying wavelengths. Red and orange light have longer wavelengths. When red light hits the water it is absorbed more strongly. Blue and violet lights, on the other hand, have shorter wavelengths. Blue is less absorbed by the water and therefore becomes more visible to our eyes as it is filtered out. This causes us to see the oceans and seas as mainly blue.
The ocean and seas can take on a variety of shades of blue because of the way light hits and then bounces off other objects in the water, including sediment. For example, greener hues will result if more algae is present. If there has been a big storm, the oceans and seas can look a lot darker in color, even brown. This is because sand and other sediment, including runoff from river, is stirred up and is closer to the surface.
Greater expanses of water can absorb more light. However, after 656 feet very little light gets through. Once a depth of 3,280 feet is reached no light penetrates. Deep water looks a lot darker because the more water light has to pass through the more it gets absorbed. Water closer to shore is usually lighter in color, even turquoise, because of the way light bounces off the floor of the ocean and other objects.