The Blue Ocean: Why Isn't a Glass of Water Blue?

Water molecules act like tiny sponges for light, but they are very picky eaters. They love to 'soak up' or absorb red, orange, and yellow light waves. When you have a small glass of water, there aren't enough molecules to soak up much light, so the light passes through unchanged and the water looks clear.

In the deep ocean, there are billions of water molecules piled on top of each other. As sunlight travels deeper, the water molecules soak up almost all the red light. The only color that isn't absorbed and can bounce back to your eyes is blue. The ocean is blue because that's the only color the water 'rejected!'

Because red light is the first to be absorbed, things start to look strange underwater. If you took a red apple 30 feet deep, it would look gray or black! This is because there is no red light left at that depth to bounce off the apple and reach your eyes. Divers often carry flashlights to bring the 'stolen' colors back to life.