Why earplugs don't affect your hearing under water

Matthew Alice: Why can I still hear underwater when I wear earplugs to keep water out of my ears? — Jake, swimming

I can understand your confusion. You certainly can’t smell underwater when you wear a nose clip to keep water out of your nose.... Anyway, when you’re underwater, sound waves zip very efficiently through the water you’re swimming in and into the water that makes up a large part of your head. (A goodly percentage of the human body is water. So basically your head turns into one great big ear. That also helps explain why it’s difficult to judge where a sound is coming from when you’re underwater. When sound travels through air, it will generally strike one ear sooner than the other, giving us a clue to direction.