A 2-metre saltwater crocodile spent several hours close to shore at Fitzroy Island off Cairns on Monday.
Fitzroy Island Resort says the sighting was "rare", but it ramped up patrols and warnings to visitors.
Queensland's environment department says it is investigating the sighting and continuing to monitor the area.
A saltwater crocodile has caused a commotion at one of Queensland's most popular tourist islands, forcing snorkellers out of the water and a resort to ramp up safety precautions.
A 2-metre croc was spotted close to the shore of Fitzroy Island, 29 kilometres off Cairns, on Monday, prompting resort and ferry staff to issue warnings and erect signage.
Far North Queensland is famous for its crocodiles, but sightings near the island are rare, with the last known occasion at the popular snorkelling and swimming spot nearly two years ago.
Fitzroy Island National Park is a 45-minute boat trip from Cairns and is popular with locals and tourists. ( Supplied: Colliers )
Bundaberg-based sailor Mark Fletcher was among those who saw the crocodile while his yacht was anchored off the island on Monday.
He was in the water to inspect a faulty propeller when he heard people screaming from the shore.
"[I] got back on the boat and there were some people standing on the staircase who had a full view of the ocean, and they were screaming out, 'Crocodile, crocodile,'" Mr Fletcher said.
He took his dinghy to the beach to investigate and was told the crocodile had been heading towards him, before changing course towards two snorkellers who got out of the water after hearing the yelling.
"I didn't really know it was in the water when I was in the water," Mr Fletcher said.
Safely back on his yacht, Mr Fletcher saw the croc pop up again a short distance away.
"It just floated along the beach, about 20 metres off, looking at people — people standing up at the back of the beach like crows on a power line — and it just floated past, not a worry in the world," he said.
Scottish tourist Kyle O'Shea, 23, described seeing the crocodile as "surreal" and a "core memory" that would stay with him forever.
He and his girlfriend travelled to the island on Monday after flying from their home in Glasgow to fulfil their dream of visiting Australia.
As the couple lined up at the Cairns marina to board their ferry to the island, a crew member advised a crocodile had been spotted that morning.
"And then when we were on the boat heading to the island, they also told us again that there was a crocodile," Mr O'Shea said.
Upon arriving at the island, they encountered more warnings from staff and on freshly erected signage.
Warning signs will remain on the island for seven days after a sighting. ( Supplied: Kyle O'Shea )
Mr O'Shea said he and his girlfriend were initially a bit disappointed their snorkelling plans had been "ruined".
"Once we get told there's a crocodile, [my partner was] just like, 'No, not a chance,'" he said.
But he said their disappointment was soon eclipsed by the excitement of seeing the crocodile "bobbing on the waves" as they were sitting on some rocks near the shore.
"Somebody pointed over and I was like, 'Oh, what's she pointing at?'" Mr O'Shea said.
"You could see everything, you could see the tail with the spikes on it.
In a statement, Fitzroy Island Resort said crocodile sightings near its shores were "rare", but it was treating the incident seriously.
It said the resort had reinforced existing safety and communication procedures, including regular shoreline inspections, ongoing checks from its vessels and regular communication with resort guests, day-tour operators and passengers.
"Although these sightings are uncommon, we are well equipped to manage them and will continue to monitor the situation closely, continuing regular contact with Parks and Wildlife authorities and following their advice," general manager Dallas Bickle said.
Queensland's Environment Department confirmed it was investigating the sighting and was continuing to monitor the area.
Mr Bickle said the crocodile was thought to be a young male searching for new territory during breeding season and had not been seen again near the island since Monday night.
He said it was the second sighting he had dealt with in his three years in the role, the last one being in late 2024.
The crocodile was a holiday highlight for Scottish tourists Kyle O'Shea and Chelsea Kerr. ( Supplied: Kyle O'Shea )
Both Mr Fletcher and Mr O'Shea said they were satisfied with the resort's handling of the situation and its efforts to warn guests.
Mr O'Shea said the experience had not deterred him from returning to Australia.
"If anything, it's inspired me to come back because Cairns is a lovely place and I just love crocodiles," he said.
