The reptile was spotted by a fisherman on a mudbank in the Mary River.
“Although there have been a number of anecdotal reports of crocodiles sighted in the Great Sandy Straits and Mary River over recent years, this is the first confirmed sighting,” Environment Minister Andrew Powell said
Traps are being set up to capture the beast, in keeping with a state government policy that dictates any croc seen south of the Boyne River in central Queensland is to be relocated to a crocodile farm or zoo.
Although the area where the crocodile was spotted is upstream from swimming spots, it is used by fishermen, and the general public have been warned to stay away from the area.
A 2010 environment department survey examined 48 rivers and found no evidence of crocs between the Fitzroy River to the north and Maryborough, which lies west of Fraser Island.
Saltwater crocodiles are the largest of all living reptiles and are highly opportunistic and territorial predators.