But after three days, and with no sign of the missing twin alive or dead, the search was called off.
Then came the twist.
The whole thing, police said, was an elaborate hoax – and there was no "twin". Never had been.
NSW Police believe the Victorian who had reported his brother missing last week had built a second identity and was planning to disappear so as to escape from his past – and debts in the millions of doillars – and start a new life as his own brother.
"Inquiries determined the report was false, and there was no missing swimmer," NSW Police said in a statement.
Officers this week issued a future court attendance notice to the man for making a false representation resulting in a police investigation.
The man is understood to be in Victoria, but he is not in custody. The police will not release his identity for privacy reasons.
He is due to appear at Bega Local Court on October 15 and is also wanted by Victoria Police on fraud charges.
"He's now wanted in two states," NSW Police South Coast District Chief Inspector Peter Volf said.
Inspector Volf said it had been a tremendous effort by emergency services and volunteers, but in the end it was "all for nought".
The three-day search may have cost emergency services more than $ 1 million.
Surf Life Saving NSW Far South Coast Cheryl McCarthy told the Bega district news it was "frustrating and disappointing" for volunteers, who gave their free time to assist in situations which often aren't safe for them.
"We had 25 people involved over the three days, all volunteers. [But] there are lots of positives here that we can look to – there's no substitute for training than the real thing. And I'm really proud of the way they worked together, "she said.
Westpac's rescue helicopter chief executive Stephen Leahy said the criminality would be left to police.
"Our job is to respond to requests for search and rescues, it's up to the police to deal with the criminality of those complaints."
But added it was unlikely the costs would be recouped, with the use of the chopper alone cost about $ 33,000.
"There were lots of resources tied up on this search. That was both financially costly and also a lot of volunteers from surf lifesaving, the SES, the marine rescue and other agencies had to take time off work to attend that search," he said .
Charlotte is a reporter for The Age.