The whale seemed to stare straight at him. Fisherman Ivan Iskenderian watched it swim within a metre of his boat in Sydney's Middle Harbour.
As the whale rose from the water, he saw a plastic bag and some fishing line stuck near its enormous mouth. He reached out his hand and snatched them away.
His friend Michael Riggio snapped a photograph of the close encounter, near Roseville Bridge, calling it a "once-in-a-lifetime" selfie.
Mr Iskenderian, 20, of Forestville, said he did not stop to think before touching the head of the massive mammal.
"It was a bit daunting but the whale was very calm," he said.
"He came up to the boat a couple of times, putting his head out of the water. There was a plastic bag and fishing line sitting on the side of his mouth, and it seemed like he wanted it taken off. So I dropped my phone, reached over and just grabbed it."
The young southern right whale then repeatedly slapped its fin on the water, he said.
"Apparently that's what they do when they're relaxed. It seemed quite happy. It could have been a kind of thank you."
Whale expert Geoff Ross said the mammal - weighing about 65 tonnes and roughly the length of a single-decker bus - deliberately came looking for a helping hand.
"It is bizarre, really unique behaviour for a wild animal, particularly for its size. But they are quite intelligent," he said.
"It approached the vessel from the stern, diving and looking at the boat before lifting its head out of the water to allow the fishermen to remove the entanglements from its lower jaw.
"It's an extraordinary animal and all the more reason why it's important to welcome large animals like this in our waterways."
The chance meeting occurred about 3.30pm on Tuesday afternoon.
Mr Iskenderian, who works in a fishing tackle shop, was returning early to Roseville boat ramp after a fruitless fishing trip for tuna beyond the heads.
He had seen the whale in the harbour several times recently. But this time it swam close to his boat and other vessels idling in the water, coming within 50 centimetres of his stern.
"He was just hanging around, bringing his eye out of the water and looking directly at us," he said.
The sound of its breathing was "immensely loud", he said.
He spied the rubbish on its head and, when it lifted its head from the water a third time, he whipped it away. Its head felt hard, he said.
"I was pretty stoked I actually got it. It was pretty good, a couple of people were clapping. That's my good deed done for the day, I guess."
Mr Riggio, a 17-year-old student from Collaroy, said the whale looked as if it wanted to play.
"It wasn't fazed by us being there at all. I took a selfie when it popped up. It was definitely a once-in-a-lifetime thing. I never thought I'd be that close to a whale."
The strange story has attracted media attention around the world.
Mr Ross, a wildlife management officer with the NSW National Parks and Wildlife Service, said the whale entered Sydney Harbour about three weeks ago and had been moving about the deeper waters around The Spit.
The young adult whale is distinguishable by the unique pattern of callosites, or white growths, on its head. Mr Ross said. Its sex is unknown.
Southern right whales were so-named because they were "right" for fishermen, who exploited their non-aggressive temperament.
"I liken them to cows, because they're quite calm and happy most of the time, but they will respond in a very aggressive fashion if they feel threatened," Mr Ross said.
"This animal has been very calm and relaxed. But on at least three occasions now, kayaks or boats have got too close and the animal has reacted quite aggressively, lashing out its tail or breaching across the surface."
Boats should not move within at least 100 metres of the whale, while swimmers shouldn't approach closer than 30 metres, he said.
"Just be respectful. We don't want to see this animal harmed and we don't want to see anyone injured. Respect the approach distances and enjoy the spectacle of having this beautiful animal in our harbour."
