Fellow diving instructor Fabian Seidel said the orca appeared as a “white shimmer”.
“These sea pandas rocked up out of bloody nowhere,” he said.
“One orca checked me out, looked me right in the eyes, scanned me, and fully interacted with me.”
Video footage posted to social media shows the incredible moment the orca swam up within arm’s reach of the divers.
Henderson, who has only worked with the diving tour operator for a few weeks, described the one-minute encounter as “epic”.
“They’re such strong, powerful animals, but also majestic and beautiful to watch and they just came so close and they’re so curious,” she said.
“You’re so shocked that you can see and appreciate them, but then also scared because they are an apex predator.
“So it’s a mix of fear and excitement because it’s such a crazy experience because you’re in the water with them.”
Henderson said the two orca were juveniles, or younger calves which made the encounter even more surprising.
“It was insane, because they do not look small,” she said.
She said the orca had been hunting stingray and playing with the bubbles left by the divers as they descended 30m toward Castle Rock.
Henderson said the divers did not reach out or attempt to touch the orca, despite being within touching distance.
“It’s like an organic experience, you don’t want to chase them or anything,” she said.
Divers from the Cathedral Cove Dive and Snorkel had a once-in-a-lifetime encounter with a pod of orca last Friday. Photo / Supplied
Henderson attained her Diploma in Professional Scuba Instructing last year, setting her up to work in her dream field.
“I was at boarding school, I wasn’t really loving it,” she said.
“I just wanted to do something different and I’ve grown up around the water and loved being in the water so I thought dive instructing would be an amazing career path.”
The Hahei resident says she loved working with Cathedral Cove Diving and Snorkel and hoped to eventually explore career opportunities overseas.
Seidel, 31, originally from Western Australia but working in New Zealand “for the season”, said he had dreamed of encountering orca his whole life.
“You can’t plan moments like this or buy encounters like that with any amount of money,” he said.
“It’s so special when they choose to hang out with you, when they genuinely want to know what you are.”