Video narration
Why does a glass of water look clear while the deep sea looks blue? Think of a swimming pool: the deeper the water, the more sunlight crosses it. Sunlight has many colors, but water absorbs red, orange, and yellow more strongly than blue. Red fades first. Blue travels farther; scattering sends it back to you. So the sky may reflect on the surface, but water creates most of the blue. That’s why deep seawater—and a deep pool—look blue.