Rare footage of a wild dolphin giving birth to a calf has been recorded south of Perth, offering a unique glimpse into the lives of the private mammals.

The birth surprised and delighted dolphin lovers at Mandurah estuary during a dolphin watching cruise.

Dolphin volunteer and rescuer Robyn Bickell saw the birth and said it was an emotional experience.

"It was very emotional — dolphins are like our little family here and so to witness a dolphin birth, it was truly an incredible experience for me," Ms Bickell said.

The dolphin calf and its mother made their way across the Peel Inlet to the Murray River. ( Supplied: Mandurah Dolphin Rescue Group )

Ms Bickell said the mother had been closely watched by Mandurah Dolphin Rescue Group and researchers.

"She's definitely been observed, she's been very big and swimming alongside the boat — we did know she was pregnant," she said.

"To see this tiny little calf taking its first breath of life was just amazing and it's something I'm never going to forget. I feel very lucky."

Ms Bickell said she saw the dolphin jumping out of the water, rolling around and having contractions, but the tour boat was careful to keep a distance away.

The mother was observed having contractions, arching her back and pushing. ( Supplied: Mandurah Dolphin Rescue Group )

"We didn't want to encroach on her at all, we kept quite a distance to stay back from her. She was in the shallow areas, we didn't want to affect the natural process," she said.

"The people on the boat gave off a loud cheer, clapping and cheering with excitement, so that was pretty special."

Rare recorded birth coincides with baby boom

Murdoch University dolphin researcher Krista Nicolson said the recording of the birth on film was extremely valuable for scientists.

"It's actually only the second observed dolphin birth in the wild — there was another one that was recorded in South Carolina in the United States in 2013 — which is really, really exciting," Ms Nicolson said.

The newest arrival is also part of a dolphin baby boom, with the region welcoming 11 newborn dolphins, including six calves born in Mandurah Estuary, one in Dawesville Cut and four along the Mandurah coast.

"We've been able to observe the newly-born individuals quite well. This particular female spends a lot of time up on the rivers," Ms Nicolson said.

"When the calf is born we often observe them being in a group of other mums and calves, then the mum will teach the young the ways of life."

Mother linked to calf euthanased last year

The adult dolphin is believed to be the mother of another baby dolphin which was euthanised last April after its mother was unable to be located.

The baby dolphin that was euthanased last year when its mother could not be found. ( ABC News: Andrew O'Connor )

"This is the third dolphin that I have observed that has lost their calf and then given birth exactly a year later," Ms Nicolson said.

"This calf is only three days off [to the year] from when her other calf was euthanised.

"It's really exciting that even though she lost the other calf that she has gotten pregnant again and had this calf."

The sex of the young calf is unknown, but it's been dubbed 'Pom Pom' by the crew on board the vessel.