Reef death probe told delay in help call

Leila Trott disappeared in choppy waves on the Great Barrier Reef but it took 40 minutes for her colleague to officially raise the alarm, a court has heard.

The 38-year-old skipper went missing while trying to retrieve a rogue dinghy off Green Island on April 6 last year.

A coronial inquest into her death heard on Wednesday that her colleague Filippo Matucci lost sight of Ms Trott after taking a "two-minute toilet break".

Mr Matucci, who will testify on Thursday, initially called his manager and took part in a search with about five nearby vessels.

But the official "pan-pan" call that would have alerted Water Police and the retrieval helicopter in Cairns was not made until 2.06pm, about 40 minutes after Ms Trott was first noticed missing.

Her lifeless body was found floating face down in the water at 2.18pm.

Senior Constable Darlene Webb said there was no evidence Ms Trott could have been saved if Mr Matucci had called the pan-pan earlier because the helicopter was down for service on the day and police would take an hour to reach the search zone.

"As tragic as it was, I couldn't find any criminality," Sen Const Webb told the Cairns Coroner's Court.

Forensic pathologist Paul Botterill said Ms Trott most likely died from a cardiac episode suddenly brought on by a significantly narrowed artery.

Dr Botterill said it was not unheard of for the underlying heart condition to cause people to die without showing symptoms.

"Certainly some people die in their sleep with this condition, some people drop suddenly with no expression of pain," he said.

The court had previously heard Ms Trott was a fit and healthy woman and an experienced swimmer who was capable to making the up to 450 metre swim to the dinghy.

Her parents Janet and Robert Trott fear the true cause of their daughter's death may have been covered up to protect tourism on the reef.

Dr Botterill said he could not exclude that Ms Trott had been stung by an Irukandji jellyfish, although no marks were found on her body.

The court heard an Irukandji sting could be hidden on the scalp or by grazing from CPR but that the symptoms usually took 30 minutes to manifest.

Mr Matucci was also not required by law to look out for Ms Trott, who was wearing a bikini and diving fins, because she was swimming, not snorkelling.

"We didn't see him being liable," Workplace Health and Safety Queensland investigating inspector Angelo Capaldi said.

The dive instructor had initially volunteered to swim the distance but Ms Trott decided to go instead because of her seniority.

French tourist Josette Grasset described Mr Matucci as looking "worried" and "very stressed" as he watched Ms Trott swim to the dinghy, which had come loose from the main boat.

The inquest continues.