Queensland Parks and Wildlife Service rangers are searching for the reptile and have installed warning signs where it was sighted at Myora Springs, just north of Dunwich on Stradbroke Island, also known as Minjerribah, on Wednesday morning.
They're sweeping the area in boats and using drones after the crocodile was reported by the local Quandamooka Yoolooburrabee Aboriginal Corporation.
"Crocodile warning signs will be installed at boat ramps while the investigation is underway," an environment department spokesperson said.
"Visitors and residents on Minjerribah are urged to stay away from Myora Springs for safety reasons and to allow rangers to complete their investigation.
"The investigation will identify if a crocodile is present on Minjerribah."
The Department of Environment and Science said if found, the crocodile would be in an area classified as an atypical habitat zone and removed regardless of its size.
Crocodiles aren't known to venture so far south in Queensland, with Minjerribah about 440km south of their regular habitat range.
Bond University marine scientist Dr Daryl McPhee said if the animal was found it would be "exceptionally rare" and a "one-in-one-hundred-year event".
"The person who reported it, I think, is highly credible. He's a local traditional owner but also somebody who's spent a lot of time on the water, so I certainly put some credibility in what he's seen," he told AAP.
"It is feasible but obviously exceptionally rare for a crocodile to be this far south."
Dr McPhee, who authored the book the Environmental History and Ecology of Moreton Bay, said a crocodile was shot dead on the Logan River in 1905 but was rumoured to be a released pet.
He said this one could have been released although it was unlikely, or it could have drifted from the most southerly known range of crocodiles in Hervey Bay.
Crocodiles can move large distances at sea, he added, particularly after flood events.
The scientist also wondered how long a crocodile could have been at Minjerribah before it was spotted and what a large three-metre animal could feed on in the area.
"So certainly any dogs in the area might have been at risk," Dr McPhee said.
"That's something we need to think more about, assuming that it is verified as a crocodile," he said.
"It's quite a large animal, three meters is bigger than I expected."
There were 41 crocodile attacks on humans, 12 of them fatal, in Queensland between 1985 and 2021.
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