Two fishers say they were pestered by a monster crocodile while on a fishing trip in far north Queensland.

Andy Thomsen and his friend were fly fishing in the Hinchinbrook Channel, south of Cardwell, last weekend when the croc first appeared, sitting high in the water near the mangroves a good distance away.

Unanchored, their boat drifted downstream but the five-metre-plus crocodile did not want to leave them alone.

To get away to a safe distance, Mr Thomsen started the motor to move not once but twice, but the beast kept on following.

The croc, then disappeared only to emerge two metres from the boat, sitting low in the water.

"He came right up to us and eyeballed us," Mr Thomsen said.

"His head was about 80 centimetres long.

"I do see a few big crocodiles, but [this] is the closest and most worrying I've ever had.

"It scared the hell out of us.

"My heart was just going."

The seasoned fisher was torn, he could either sit tight on the boat, or restart the motor to get away - that however would require moving to the starter motor which was even closer to the croc.

"He could quite easily lunge two metres," Mr Thomsen said.

The fishers yelled at the croc and shoed it away with their arms, prompting it to slink back underwater.

It is breeding season and Mr Thomsen said he believed the crocodile was warning them that they were in its territory.

"If we had been in a smaller boat or a kayak this crocodile would have attacked us for sure trying to maintain dominance in its territory," he said.