Local resident Rob Minshull told BBC News of the reports as he gave a first-person account of living through the ongoing floods in the Australian city.
Minshull said: "Right now I'm looking at a car floating past my house; I can see fridges, furniture, sofas - there's even been a report of a shark sighted.
"It was a bull shark and it was spotted in a local suburban street. We do have sharks in the Brisbane River - they have obviously come over the flood barriers and come looking for food."
Thousands of people have been evacuated from their homes in Queensland since the flooding began in the region last month.