Experts have sounded a warning about the presence of aggressive bull sharks on Australia's east coast just months after a string of attacks in Sydney.
The grim warning follows a horrific start to 2026, when four people were attacked in just 48 hours, including three people in the Harbour City.
Heavy rainfall and murky water were blamed for the spike, which turned deadly when 12-year-old Nico Antic was fatally attacked while jumping off rocks at Shark Beach near Vaucluse in Sydney Harbour on January 18.
The following day, surfer Andre de Ruyter, 27, survived a terrifying encounter at Manly Beach and suffered catastrophic leg injuries that resulted in amputation.
That same day in Dee Why, an 11-year-old boy had his board bitten but escaped uninjured, a near-miss that underscored the growing danger.
On January 20, a 39-year-old surfer survived after a shark bit his chest and board at Point Plomer on the Mid North Coast.
In September 2025, experienced surfer Mercury Psillakis, 57, was killed by a great white shark in Dee Why, the second fatal attack in the area since 1963.
NSW SharkSmart has warned nutrient‑rich run‑off can cloud the water, draw in baitfish and create prime hunting conditions for ambush predators like bull sharks, sharply increasing the risk of an encounter.
Beaches across Sydney were closed in January following a horror spate of attacks in 48 hours
Shark expert Chris Pepin‑Neff (pictured) warned whatever was stirred up in January likely hasn't disappeared, meaning the risk of shark encounters could still be elevated
Police are seen at the scene of a shark attack at Manly Beach in January
University of Sydney shark expert Chris Pepin‑Neff has welcome the warning about potentially increased shark activity, in stark contrast to January when no alert was issued until after two attacks on January 19.
He said the cluster of incidents was highly unusual, with researchers now examining whether the 127mm of rain that lashed Sydney in a single day created 'unique' conditions that drew in bait fish and, in turn, bull sharks.
'My educated guess is that there was an additional variable from that heavy rainfall event that stirred up something that lured more bait fish and subsequently bull sharks,' he told the Daily Mail.
'There may have been something on the ocean or Harbour floor that was disturbed, giving bait fish something they were excited to feed on and that drew in the sharks.
'We've had plenty of heavy rainfall events in Sydney before, so why was this one different? For so many sharks to move inshore, something unusual was happening - we just don't know exactly what yet.
'Whatever was stirred up in January likely hasn't disappeared, meaning the risk of shark encounters could still be elevated.'
Pepin‑Neff added data also pointed to increased great white shark activity along Sydney's northern beaches.
'People should look at the apps before going into the water because as water temperatures drop, bull sharks move up the coast to the Brisbane River, but great whites prefer colder temperatures and move in,' he said.
Shark attack survivor Andre de Ruyter (pictured) made a miraculous recovery after he was mauled by a shark at Manly Beach in January
In September 2025, experienced surfer Mercury Psillakis, 57, was killed by a great white shark in Dee Why, the second fatal attack in the area since 1963
'It's been a tragic and very sharky season and we need to be aware.'
Scientists from the NSW Department of Primary Industries, who have been tagging bull sharks since 2009, said water temperature is a key predictor of their presence.
When water temperatures dip below 19 degrees, bull sharks leave the cold waters of Sydney Harbour behind and travel north to Queensland for winter and spring.
Dr Vanessa Pirotta said the January attacks highlighted the need for accessible information and education about ocean conditions and marine life.
'Like we check the UV index, checking environmental conditions should also be part of that,' she told the Daily Mail.
'If people are informed through science, this can help people make good decisions on how to interact with the sea.
'Ultimately, it is an individual choice as to how people interact with the environment.'
Dr Pirotta warned the current whale season means a heightened potential for dead whales to increase shark activity.
Marine scientist Dr Vanessa Pirotta (pictured) said people should check environmental conditions before swimming in the ocean similar to checking the UV index
Shark nets have long been used to protect swimmers along the east coast, but critics argue they're ineffective and kill large amounts of marine life, fuelling a growing debate over whether they should be scrapped.
The Fisheries Scientific Committee has argued the NSW shark meshing program was a major environmental threat to grey nurse and great white sharks.
However, it stopped short of recommending nets be removed.
Pepin-Neff said shark nets are 'ringing the dinner bell' for apex predators and should be removed.
'They don't have a single study to show they have prevented an attack. I have five studies that show gill nets attract sharks,' he said.
'I think politicians are concerned that if they support removing the nets and then there is an incident they will lose their seat.'
Shark meshing on beaches along Sydney's coastline began in 1937. Now there are 51 beaches across approximately 200km of coastline that are meshed.
Fisheries Scientific Committee chair Dr Patricia Dixon said around 40 per cent of shark entanglements occur on the beach side of the nets because sharks are able to swim over and around the nets.