I commend you on your research skills. Mike Opal of Charlestown is our winner , he was picked from the long list of correct answers. The white light is composed of various shades like all the colors of the rainbow. But seawater doesn't absorb blue light, so the blue light is reflected outwards causing the blueish color. Answer taken from Boston Harbor Cruises Web Site where we got the question.
Sea water absorbs all the reds, yellows and greens out of the water.
That leaves only blue light to be reflected by the water molecules. You may notice that sometimes, water looks green. That's because the blue water mixes with the yellow pigments in floating plants. Well, that got its name because, similar to green water, that area contains seasonal algae blooms that color the surface water red. The ocean is blue because water molecules resonate at the frequency of blue light waves.