A possible fourth and previously unreported shark attack at Cid Harbour in north Queensland has come to light in high-level State Government emails obtained by the ABC.

Key points: Emails reveal an unverified Cid Harbour shark bite shortly before the first reported attack in 2018

Emails reveal an unverified Cid Harbour shark bite shortly before the first reported attack in 2018 Three drum lines were set after a 12-year-old girl was attacked

Three drum lines were set after a 12-year-old girl was attacked The drum lines caught six sharks but were removed more than a month before the fatal attack on Dr Daniel Christidis

The alleged attack occurred shortly before three attacks in the same location in late 2018.

Documents obtained through a Right to Information request also show the idea for "no swimming" signs at Cid Harbour on Whitsunday Island was only raised by government officials the morning after the fatal shark attack on Victorian medical researcher Dr Daniel Christidis, despite questions being asked weeks earlier about whether a swimming ban should in place.

Queensland Boating and Fisheries Patrol acting district manager Craig Bambling emailed senior departmental officials about Cid Harbour on September 20.

"The media have been asking local marina staff if anyone is going to issue a direction for no swimming at Cid Harbour," he wrote.

The email was sent hours after the attack on 12-year-old Hannah Papps in Cid Harbour — the second shark mauling in 24 hours.

Word then spread of another suspected attack.

Timeline of attacks: September 10: Previously unreported shark attack on boatie at Cid Harbour.

Previously unreported shark attack on boatie at Cid Harbour. September 19: Justine Barwick, 46, attacked while swimming at Cid Harbour.

Justine Barwick, 46, attacked while swimming at Cid Harbour. September 20: Hannah Papps, 12, attacked while swimming at Cid Harbour. Media ask if Cid Harbour should be declared no-swim zone.

Hannah Papps, 12, attacked while swimming at Cid Harbour. Media ask if Cid Harbour should be declared no-swim zone. September 21: Three drumlines deployed.

Three drumlines deployed. September 22: School holidays begin.

School holidays begin. September 27: Drumlines removed.

Drumlines removed. October 7: School holidays end.

School holidays end. November 5: Dr Daniel Christidis, 33, attacked and killed while swimming at Cid Harbour.

Dr Daniel Christidis, 33, attacked and killed while swimming at Cid Harbour. November 6: Queensland Government statement about signs: "The Department of Agriculture and Fisheries will install temporary signs by the weekend with permanent signs to be installed within the next few weeks," Kate Jones.

Queensland Government statement about signs: "The Department of Agriculture and Fisheries will install temporary signs by the weekend with permanent signs to be installed within the next few weeks," Kate Jones. November 9: Expert roundtable; Government releases five-point plan including recommending Cid Harbour as a "no swim zone".

"There was another shark incident 10 days ago in the same location," Fisheries Queensland executive director Claire Anderson wrote in an email to senior officials in the Department of Agriculture and Fisheries and the Premier's Department, also on September 20.

"A local boatie was bitten but strapped himself up and took himself off the (sic) hospital. There are comments on social media about it so it will likely be picked up by media," Ms Anderson wrote.

"This reinforces the need to get some drum lines in the location as quickly as possible."

The attack on the boatie could not be verified, but three drum lines were set the following day.

The lines caught six sharks — five of them tiger sharks at least 2 metres in length.

The State Government, worried about the start of school holidays, also sent patrols to Cid Harbour to travel boat-to-boat warning of the danger of swimming at Cid Harbour.

But on October 3, Agriculture and Fisheries Minister Mark Furner signed off on a decision to remove the drum lines, noting complaints about them, and to cease patrols when school holidays finished on October 6.

In a ministerial briefing that day, he was reassured that "widespread publicity and at-sea advice from QBFP means that most users of the area should be aware of the situation".

But he was also warned there was a risk of further shark attacks.

"The only way of totally avoiding the risk is to not swim in the area and this can only be achieved by public education," the briefing said.

Warning signs and marine marker buoys at Cid Harbour in November 2018. ( Twitter: DAF Media )

It made no mention of signage, instead seeking to rely on social media and "seeking the support of the charter boat operators to warn clients of the risk".

Daniel Christidis was "a fantastic doctor" to his patients, Professor O'Connell said. ( Twitter )

Dr Daniel Christidis was on one of those charters on November 5 when he went paddle-boarding with a friend at Cid Harbour.

As they took turns on the board, Dr Christidis, 33, was attacked by a shark while in the water about 5:30pm, suffering significant wounds.

Despite almost immediate medical care, he died from his injuries.

At 6:52am the next morning, Ms Andersen — now acting deputy director-general of Agriculture and Fisheries — raised the idea of banning swimming at Cid Harbour.

"Is it possible for MSQ or police or ports to make the harbour a no-swimming zone and put up signs?" she asked in a November 6 email to colleagues.

Cid Harbour on Whitsunday Island was declared a no-swim zone after a series of shark attacks, the last one fatal. ( ABC News: Tara Cassidy )

"There are other areas of Qld where swimming is banned. This might be a better alternative to drum lines as it is known to be notoriously unsafe???"

Tasmanian tourist Justine Barwick was also attacked by a shark in Cid Harbour. ( Supplied: Family Based Care )

Within two hours, a ministerial staffer responded, saying: "Premier's keen on the signage option."

Signs 'not good enough'

The Opposition remains highly critical of the Government's response to the attacks.

"In our view, signs don't go far enough," Deputy Opposition Leader Tim Mander said.

"Drum lines should have never been withdrawn. There should have been an intentional shark control program, because people's safety comes before sharks."