Quote: "Lakes and oceans appear blue for several reasons. One is that the surface of the water reflects the color of the sky. While this reflection contributes to the observed color, it is not the sole reason.

Some of the light, hitting the surface of ocean, is reflected back directly but most of it penetrates the water surface interacting with its molecules. The water molecule can vibrate in three different modes when light hits it. The red, orange, yellow, and green wavelengths of light are absorbed so that the remaining light we see is composed of the shorter wavelength blues and violets. This is the main reason why ocean color is blue."

https://en.wikipedia.org/wiki/Color_of_water