"I was actually quite relaxed, I knew it was (not a shark) because the fin was quite long and black in colour. It was a really, really good experience."
Twenty minutes later, two orca returned and De Jongh's wife, Deonette, was ready with a camera.
The video, which has more than 8000 views on YouTube, shows a frightened diver scrambling on to a rock. He whips off his goggles and peers frantically around at the murky water.
The orca loses interest in the man and turns towards a curious labrador in the water. Within seconds, the dog turns and paddles for land as the orca follows.
In another bystander's video, taken from a different angle, a man throws sticks - apparently encouraging the dog back into the water.
His actions have been condemned by the SPCA as "irresponsible and stupid".
Orca expert Dr Ingrid Visser said it was common for New Zealand orca to approach the shore to hunt for sting-ray.
She said the mammals can tell the difference between sting-rays, humans and dogs.
