A strong storm system in the Southern Ocean will bring swells as high as 7 metres off Australia's southern coastline ahead of the weekend, creating dangerous conditions for fishing, surfing and boating.
The "very large south-west swells" are expected to hit Victoria, Tasmania and South Australia on Friday before easing on Saturday.
Tragedy had already struck South Australia during the Easter break when a father and daughter were swept off rocks at the Whaler's Way Sanctuary at Cape Carnot, south of Port Lincoln, on Sunday.
In Victoria, the Rip Curl Pro, at Bell's Beach near Torquay, was put on hold today as organisers wait for a bump in swell.
South Australian Bureau of Meteorology forecaster Matt Colopy said the swells would average between 5 to 7 metres in height across the exposed South Australian coast but could double in size during some swell sets.
He said swell in Victoria could reach up to 9 metres and Tasmania was expected to "get the brunt of this system".
"What is causing this swell is a really strong low in the Southern Ocean," he said.
"So it's really a long way away and this swell travels across the Southern Ocean and is likely to reach our coast early on Friday morning and increase quite rapidly during the day.
"It means any exposed coast around the South-East, and Kangaroo Island, is going to see very large south-west swell, as well as around the beaches and any rocky coastline and cliffs will be exposed to those very large swell conditions.
"That swell will push up into the SA gulfs where a lot of people do their boating, surfing and fishing.
"They won't be quite as large as they push up into those more-sheltered waters but still very significant for those parts of our SA coast."
Mr Colopy advised people to avoid swimming in waters off the South-East, Kangaroo Island and the southern tips of the Yorke and Eyre peninsulas.
"They really do see the brunt of these south-west swells," he said.
Conditions can 'change quickly'
He said two-metre high tides would also contribute to more water hitting the coastline.
"Certainly the swell event happening on Friday— if you look at the swell at 6:30am, there's only 2 to 3 metres of swell on southern Kangaroo Island and six hours later, that's nearly 6 metres of swell in a short space of time," he said.
But he said the bureau measured in average wave height and there could be sets of waves that double the average.
"You might go to an exposed beach and say, 'Oh, the waves aren't too bad' and then a huge set will come in 10 minutes later so that's a very dangerous situation."
State Emergency Service deputy chief officer Dermot Barry agreed, saying people were more exposed to beach and boating activities during the school holidays and Easter break.
"Enjoy the weather but be conscious that although it seems like a nice benign day, what we do know is that it will change and that a big swell is coming in," he said.
"Although it is inviting, just be conscious not to get out there and take too many risks."
He urged people to be careful when fishing from rocks because an unexpected wave could lead to tragedy.
Surf Life Saving SA chief executive Damien Marangon said crews would be ready to respond to any emergency if needed.
"Things can change quite quickly and dramatically and with the swell that's predicted, there may be some people attracted to that," he said.
"But we just want to say to everyone that it's important to look out for one another.
"And as attractive as it may be to go out there, the thing that has to come first is your own safety and that of your loved ones."ABC