Video captures orca stalking swimmer in Wellington

A swimmer who had a close encounter with orca in Wellington's Lyall Bay yesterday was never in danger, an orca expert says.

The person who sent the video, Rebecca Parlett, said the swimmer was unaware he was being followed by two of the ocean's top predators until being alerted by other beachgoers.

He told them he turned around at one point and could have touched one.

Marine biologist and orca expert Ingrid Visser said it was hard to determine from the short video what the orca were doing, but said there did not appear to be anything alarming in their behaviour.

"I don't see any aggression, I don't see any attacking behaviour. They might have been following the swimmer - if what the person who took the video said is correct - but orca are a top predator and it's in their nature to be curious," Dr Visser said.

"It's the difference between a puppy playing and a dog attacking."

There were numerous instances of orca being around swimmers in New Zealand, but it was illegal to willingly get in the water with them.

"However, if you are in the water and they approach you, the best thing to do is to remain calm.

"There are no verified instances of orca attacking humans in the wild, but there are over 100 instances on record in captivity."