The co-owner of a popular but treacherous tourist hotspot along a rugged stretch of South Australia's coastline is considering blocking access to the site after the drowning of two people.

Key points: A father and daughter were swept off rocks south of Port Lincoln on Sunday

A father and daughter were swept off rocks south of Port Lincoln on Sunday A witness rushed to help but believes her son saved her life by holding her back

A witness rushed to help but believes her son saved her life by holding her back The co-owner of the site is considering ways to prevent future deaths, including preventing access

A 35-year-old man from Holden Hill in suburban Adelaide and his five-year-old daughter were swept off rocks at the Whaler's Way Sanctuary at Cape Carnot, south of Port Lincoln, on Sunday afternoon.

A witness told the ABC the pair, who were accompanied by a friend, were not taking photos but were walking near the entrance to a cave when a freak wave knocked them into the water.

The girl's body was recovered on Sunday night but rough conditions meant her father's body could not be retrieved until Monday morning.

Glenn Theakstone, the co-owner of Whaler's Way Sanctuary, said six people have drowned along that stretch of coast since the sanctuary opened almost 50 years ago.

He said he and his family now faced a difficult decision about the site's future.

"That's the question we're asking ourselves … do we close it or do we just close that one site?" he told ABC Radio Adelaide.

"Millions of people have been through Whaler's in that 50 years and it's a well-known icon of Eyre Peninsula.

"A lot of people come to Port Lincoln just to see that, so it doesn't just affect us — it affects the locals as well, so it's a hard decision to make."

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 37 seconds 37 s Rough weather hampered emergency crews in their search for the pair. ( ABC News )

Signage in parts of the park already warns sightseers the coast can be treacherous, but Mr Theakstone said improving warning signs was an option.

"There are places there we have fenced, put safety fences up on certain areas, and what we've found is you'll go down there and people just walk around the ends of them," he said.

"People will still go do it — it comes back down to how do we educate the people of Australia about the ocean?"

'It felt like forever'

Cape Carnot is a popular spot for selfies because of its striking rock formations, cliffs, caves and waves.

Initially it was suspected the two recent victims were taking photos, but witness Tamar Haldane — who was metres away when the accident happened — was adamant that was not the case.

"They weren't taking photos, they were just looking into the cave," she said.

"They were most probably looking at my kids playing in the cave.

"They were literally standing where I was standing with my children moments beforehand. They were doing nothing wrong."

Tamar Haldane took this photo of her children shortly before the drownings. ( Supplied: Tamar Haldane )

Ms Haldane, who is from Port Augusta, did not see the moment the wave hit the pair, but watched in shock as it pulled them under.

"As I took a step out of the cave, I could see these people. [For] a split second I thought 'why are they playing in the water'," she said.

"They were tumbling and that's when I screamed and I heard my kids scream.

"It was so quick but it felt like forever."

Ms Haldane said her "mother's instinct" kicked in and she made her way towards the water's edge, preparing to jump in.

"I started running towards the people and I screamed at my eldest son because I could see him running," she said.

"He screamed and ran towards me and said 'Mum it's too late, it's too late'."

The area is renowned for its spectacular views. ( Facebook: Renee Jacobs-Mitchell )

She said her son Jordan held her back and almost certainly saved her life.

"I have no doubt about that. My son saved my life because he knows what I'm like. He knew when he saw me running and he grabbed me, he knew that I was heading to the little girl," she said.

"He saved his brothers and sisters as well. He screamed at them to get into the cave further because it was a freak wave, that wave."

Ms Haldane said Cape Carnot "is a beautiful spot" and supported calls for better signage.