This happens because the pressure in the water is much greater than the pressure inside your ear, so the air presses onto the cartilage flaps on the inside of your ear, and then, that's why it starts to hurt.
in fact it does. try carring a 5 gallong jug of water. dive deep into the sea, the deeper you go the more your ears hurt. that is done by the atmospheric preassure the water applies to any object depending its depth. This in easy words is weight.
Because as you dive down your eardrum is being stretched by the external pressure. If, when you first feel the discomfort, you hold your nose and blow out your ears, the pain will go way as you will then have equalized the pressures across the eardrum. SCUBA divers have to learn how to do this.
To go under water they close their ears and nostrils. An adult hippo can stay under water for up to 6 minutes!
scuba diving
you are supposed to put them in "streamline" position (which means have them up over your head pressed against your ears) and dive with your hands cutting into the water first then your head and so on.
During the deep dive the divers body goes through immense pressure. The atmospheric pressure in the deep as one goes more deep it increases so the lungs of the diver has to do more work and also that if the diver comes up on surface faster ten the rate he went down then the helim would be formed in the lungs of diver which can be lethal.
They have (inner) ears.
your ears will start to hurt underwater because the water pressure is getting stronger pushing against your inner ear causing an uncomfortable sensation.
Water gets stuck in your ears when you stay under water too long.
Sea otters have closable ears that help them maintain their buoyancy and keep water out while they are swimming and diving. When they dive underwater to forage for food, they can close their ears to prevent water from entering, allowing them to focus on hunting without distraction. Additionally, their ears help them regulate body temperature by minimizing heat loss in cold waters.
there ears and there mouth get seeled so thet they can be under water for about 15-20 minuts
Because the water is forcing bubbles from you and it is sucking all the air out of your ears which causes the pressure to hurt.