A great white shark mauled 35-year-old swimmer Leah Stewart at Sydney's Coogee Beach on Saturday, and the ripple effect is already reshaping how surfers and swimmers approach the water.

Stewart, a young mother, remains in critical but stable condition at St Vincent's Hospital after multiple surgeries, including the amputation of an arm. Her family says they're "shocked and devastated".

For veteran surfer Nick Carroll, 66, who's spent more than 50 years chasing waves on Sydney's northern beaches, the attack is the latest in a string of encounters that have spooked even the most experienced ocean-goers.

Carroll, a surf journalist and lifesaver, says the attack comes at a fragile moment. After the death of Mercury Psillakis, 57, at Dee Why in September, many surfers gradually returned to the water — hyperaware but willing. Then came the bull shark attacks in late January, which Carroll describes as having a "seismic effect" on everyone.

"People had just begun to relax in the last two to three months … I think a lot of surfers had dived back in," he said. "Now this attack in Coogee has come as a real shock. There will be a lot of people who will change their habits again, and it will take months for them to get over it."

Carroll expects beachgoers will drift back, but he warns against swimming or surfing alone, and urges people to avoid the water after heavy rain when visibility is poor. He says dangerous shark encounters are still rare, but he hopes the Department of Primary Industries' shark science experts will offer more public guidance before next summer.

North Bondi real estate agent and surfer Ric Serrao was keen to try his new custom Pyzel surfboard at Bondi Beach hours after the Coogee attack. He felt cautious but confident — until a jet-ski rider told him three sharks had been spotted at nearby McKenzie's Bay minutes earlier. The trio called it quits.

"Has it stopped people? Not in my network. I think people are still going out [if the beaches are open]. Bondi was a ghost town on Saturday, but there was also no swell," Serrao said. "I can assure you if there was swell, we all would have been out there surfing and just been a bit more wary."

Still, Serrao has changed his habits. He now avoids surfing when no one else is in the water or conditions are murky, skips sunrise and sunset, and is paying more attention to his surroundings. He's also fitted a shark band to his board. "It's definitely been on our minds. Yes, I'm a lightweight, but a little bit of self-preservation doesn't hurt."

Surfer Nigel Riley, also from Bondi, is still getting in the water but is more selective about conditions. He supports a shark cull and says potential dangers play on his mind "every surf". He's got shark eyes on all his boards and dive gear, and a shark band. "Six months ago I was in the surf, it was unreal, there was salmon everywhere, and I thought, 'whatever'. Nowadays if I see salmon, I'm straight out of the water."

Independent Pittwater MP Jacqui Scruby's office surveyed more than 780 northern beaches residents and found 93 per cent are concerned about shark activity. A striking 86 per cent say they're now avoiding the water, changing the times they enter, or choosing different locations. Seventy-eight per cent feel safer when shark-spotting drones are flying, and 82 per cent support increased drone surveillance. Many reported feeling too scared to enter the water at all.

Surfers on the northern beaches have also been tracking confirmed and suspected shark encounters themselves, trying to fill what they see as a data gap on what they say is an increasingly frequent phenomenon. The survey found significant frustration that drones aren't flying at the times surfers most use the ocean.

Scruby is pushing to amend the Fisheries Management Act to require the protection of human life in coastal waters, particularly when it comes to interactions with marine predators.

For now, the message from those who know the ocean best is simple: be aware, don't go alone, and if you see salmon — get out.