A Northern Territory fisherman has reached what some would call the pinnacle of fishing by catching a metre-long barramundi in a waterhole not much bigger than a bathtub.

Leigh McNair told ABC's Tales From The Tinny that while fishing part of the Roper River, more than 400 kilometres south of Darwin, he heard the unmistakeable sound of large barramundi feeding nearby.

Unfortunately for him, the fish of his dreams was locked in an inaccessible area surrounded by thick foliage.

"You could see a few little black bream getting around and I knew there were big fish in there," Mr McNair said.

"I tried fishing it for a while but it was just too hard, the pandanus [palm] was really thick."

He said after clearing some of the pandanus away a waterhole of about 1.5 metres opened up before him.

And no sooner than he put his lure in the water did the monster fish jump into action.

"It was an unreal fight — it was like it was just bouncing off the pandanus," he said.

"It was flicking water all over the bank and mud all over me."

With the fish on the line but still far from secure, Mr McNair sent his friend Jimmy to fetch a net.

As his friend fumbled with both net and fish, Mr McNair said he began to fear two things: losing the fish and the presence of crocodiles.

"I knew there was a big croc somewhere in the system [because] I'd seen a big slide," he said.

Thankfully Jimmy was able to safely net the fish and bring it up the bank, but Mr McNair's odyssey was still not over.

To prove his merit as a fisherman he needed to measure the fish and get a photograph — something the barramundi had no intention of cooperating with.

"It started flicking around in the net and then it's cut straight through and slid down the bank towards the water," Mr McNair said.

He said after once again retrieving the fish, measuring it and posing for a photo, they returned the leviathan to its natural habitat.

Perhaps ironically the only harm done to fish or man was to Mr McNair.

"I've got a nice little scar just above my left nipple from the back dorsal [fin]; it absolutely smashed me while I was holding it for a photo," he said.