Phorcys’s laugh seemed to come from all around them. “What a coincidence! It’s also where I’m strongest. This tank is specially designed to contain demigods. Now, have fun, you two. I’ll see you at feeding time!”
The glass dome shattered, and the water crashed in.
Percy held his breath until he couldn’t stand it. When he finally filled his lungs with water, it felt just like normal breathing. The water pressure didn’t bother him. His clothes didn’t even get wet. His underwater abilities were as good as ever.
It’s just a stupid phobia, he assured himself. I’m not going to drown.

The Mark of Athena, Chapter XVI