Two large crocodiles had reportedly been seen in the area
Rangers are searching for a 62-year old man thought to have been grabbed by a crocodile.
Arthur Booker, reported to be a Vietnam veteran, disappeared near the north Queensland town of Cooktown in an area dubbed "Cape Crocodile".
Local media said Mr Booker had gone to the river to check on a crab pot, leaving his wife waiting in the car.
Police said they could not be sure a crocodile had taken Mr Booker, but had found his belongings on the riverbank.
Mr Booker is believed to have been born in Banffshire, Scotland.
Rangers at the Endeavour River campsite where the Bookers had been staying said they believed a 5.5 metre (18 feet) crocodile they have named Charlie could be responsible.
Mr Booker's camera was left on the bank, skid marks from what appeared to be crocodile feet were visible and the rope that had been holding the crab pot was frayed rather than cut, police said.
Local officials said two large crocodiles had been seen in the area and searchers needed to ensure their own safety.
"They will be looking in the water today and having a look at the bottom to see if they can't pull anything off the bottom," Queensland Parks and Wildlife Service regional manager James Newman said.
"We need to make sure the searchers are safe while they're doing the search. What we're advising is that they have someone holding their belt at all times when they're leaning over the edge of the boat," he told the Australian Broadcasting Corporation.
The area is notorious for crocodile attacks.
"You would never get me in the water around here," Duncan Faichney, who has fished in the area for 40 years, told The Australian newspaper.
"There's crocodile all around here. You don't go near them and they won't eat you - that's the deal," he said.
The last fatal attack was in August 2005 when a man was dragged from his canoe. Three days later, searchers found his torn shirt, shorts and thigh bone.
Ten months before that, the newspaper reported, grandmother Alicia Sorohan made world news when she jumped on the back of a crocodile to save a fellow camper. She earned a national heroism award and the sobriquet "Granny Dundee", after the iconic Australian movie character Crocodile Dundee.
Locals say that ever since shooting of crocodiles stopped in 1974, attacks have been on the increase.
Family members looked on in horror when Cassey Bond swam out to a ferry to help repair it in 1993. He never made it, screaming "help me!" before disappearing under water.
Baryl Wruck never returned from a boat party with friends in 1985. Leaning over the side of the boat, a flurry and splash of water heralded her demise.
A crocodile was later caught and female body parts found in its stomach, but experts could not confirm they were hers.