Old school term that still applies to today. It is the act of ejaculating while the penis is completely under water. This can be in the tub or especially in a swimming pool or larger body of water. Basically one cums under the water and the semen beads off and suspends itself under the water, slowly floating to the surface. For those familiar with the practice and have developed the fetish, they usually go after the suspended semen and try to eat the ejaculate. This does take some skill, patience, and appeal so that is why the action has been called pearl diving
I asked him if he has ever been PEARL DIVING before and he said no. So with that I let my massive load escape under the calm waters of our spa. I then motioned him to get in and told him "happy hunting".