<P> The "color" of the ocean is determined by the interactions of incident light with substances or particles present in the water . White light from the sun is made up of a combination of colors that are broken apart by water droplets in a "rainbow" spectrum . Large quantities of water, even in a swimming pool, would appear blue as well . When light hits the water surface, the different colors are absorbed, transmitted, scattered, or reflected in differing intensities by water molecules and other so - called optically - active constituents in suspension in the upper layer of the ocean . The reason that open ocean waters often appear blue is due to the absorption and scattering of light . The blue wavelengths of light are scattered, similar to the scattering of blue light in the sky but absorption is a much larger factor than scattering for the clear ocean water . In water, absorption is strong in the red and weak in the blue and so red light is absorbed quickly in the ocean leaving blue . Almost all sunlight that enters the ocean is absorbed, except very close to the coast . The red, yellow, and green wavelengths of sunlight are absorbed by water molecules in the ocean . When sunlight hits the ocean, some of the light is reflected back directly, but most of it penetrates the ocean surface and interacts with the water molecules that it encounters . The red, orange, yellow, and green wavelengths of light are absorbed and so the remaining light we see is composed of the shorter wavelength blues and violets . </P> <P> If there are any particles suspended in the water, they will increase the scattering of light . In coastal areas, runoff from rivers, resuspension of sand and silt from the bottom by tides, waves, and storms and a number of other substances can change the color of the near - shore waters . Some types of particles can also contain substances that absorb certain wavelengths of light, which alters its characteristics . For example, microscopic marine algae, called phytoplankton, have the capacity to absorb light in the blue and red region of the spectrum owing to specific pigments like chlorophyll . Accordingly, as the concentration of phytoplankton increases in the water, the color of the water shifts toward the green part of the spectrum . Fine mineral particles like sediment absorb light in the blue part of the spectrum, causing the water to turn brownish if there is a massive sediment load . </P>

Where does the sea get its colour from