The father of a New Zealand man who saved a baby humpback whale from a tangled cray pot line says his son wouldn't have thought twice about going to the rescue.

Charter boat skipper Joe Brogan, from Whitianga, was on boat off Geraldton, Western Australia last week when he came across the whale with ropes tangled around its tail.

Part of the event was filmed and posted on YouTube yesterday and shows people on board pulling the rope up onto the boat. The 42-year-old then jumps into the ocean, swims toward the whale and cuts the rope with a knife.

Mr Brogan's father, Paddy, says his son called him shortly after the incident told him of the encounter.

He believes the whale knew what was happening because it had calmed down as his son swam toward it.

His son wouldn't have thought twice about getting into the water, Mr Brogan says.

"If he'd thought about it, he wouldn’t have done it. The whale was in the shit, so he jumped in and did it," Mr Brogan says.

"[He said] it was a wonderful feeling having done that."

Mr Brogan has worked as a skipper for around six years and has a company based in Whitianga. However, he has been contracted to skipper larger boats for game fishing in Australia.

3 News