David Attenborough’s Great Barrier Reef could be the veteran broadcaster’s last on-the-road documentary, according to series producer Anthony Geffen.

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Geffen has collaborated with the 89-year-old on 11 projects over the past seven years, including Rise of Animals, Flying Monsters 3D, Galapagos 3D, and Natural History Museum Alive 3D. He is the first producer to have won three Emmys in a single year, for the 2010 series David Attenborough’s First Life.

Before Sunday’s Australian premiere of the new series on the ABC, Geffen told Guardian Australia that it’s unlikely Attenborough would do anything as ambitious and taxing again.

“In a way I feel this one is the last of what I call ‘on-the-road’ David Attenboroughs,” he said. “That does not mean this is his last film, because he’ll top and tail films, and he’ll do narrations forever. But I think the idea of taking Attenborough ... for a year to two years on a project where he’s involved intensely and goes on locations a lot throughout – I think at 90, that can’t go on forever.”

The producer fell shy of definitive statements, preferring to leave the question open-ended: “Will he stop? No, he’ll never stop. In fact he’s often said to me ... the best way to go would be on the road ... In some ways I hope that’s the case, because that’s what he loves: he loves being out there.”

Facebook Twitter Pinterest David Attenborough prepares to dive the Great Barrier Reef in 1957, for the BBC’s Zoo Quest for the Paradise Birds Photograph: BBC

The three-part series takes a groundbreaking look at the Great Barrier Reef: its formation, its ecosystems, its beauty and the various dangers it faces, from human impact and climate change. Geffen says Attenborough spent a month on location for the series, which was in production for more than two years. The story tying it together is a personal one: Attenborough first dived on the reef in 1957, and had always wanted to go back.

“I’d done 10 projects with David and I said to him, ‘Right, OK, at some point we’re going to have to have our last project together. If we’ve got one project left, where would you go?’,” Geffen said. “Without batting an eyelid he said, ‘The Great Barrier Reef ... it’s the place I still think is the most extraordinary place on the planet.’”

Each episode is followed by making-of shorts. In the first, Attenborough is filmed climbing into the Triton Submersible – a small, high-tech submarine that can dive to depths of 1,000 metres, and is the first of its kind to visit the reef. “There are lots of worries when you put your 88-year-old presenter in something like this,” Geffen says to the camera. “There are all sorts of things that can go wrong.” Series director Mike Davis adds: “We were sightly worried about how he might get into the sub.”

The crew look tense as they watch Attenborough approach the submarine from its top, making his way through the lid with first one foot, then the other. Finally he slides in, laughing: “I nearly sat on the pilot!”

Facebook Twitter Pinterest The Triton Submersible, and Sir David Attenborough within it, is lowered into the Great Barrier Reef Photograph: Freddie Claire

“I was only nervous because it was a big moment,” Geffen said. “We’d brought this sub from the other side of the world, and when somebody’s 90, you’ve got to protect them.

“I set the barriers and things, because I’m not sure David can do [all] this; I kind of over-protect the situation. And then he defies it by popping into the submarine, which is perfect!”

Geffen said while Attenborough might not be as involved in future documentaries, he won’t be missing from our screens. “I think that what you’ll get now, it’s interesting: you’ll get him sort of branding various BBC series which he has been less involved in – there’s some big new BBC series that I think he’s skinning. He tops and tails it as the sort of figurehead, and then does the narration.

“But I don’t think you’ll get the intense, what I call ‘proper’ Attenborough series, where he properly researches it with you, and writes it.”

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Geffen carefully added that you should never say never; in 2002, Attenborough himself announced he would be retiring at 80 – but it never transpired. “I mean for seven years I’ve always thought we might be making the last Attenborough series, and I’m wrong,” Geffen laughed, before backtracking once again: “And he’ll go on forever, I never want to give the – he’s not going to stop, he’s never going to retire.”

In December 2014, the broadcaster himself echoed this sentiment: “I could go on forever,” Attenborough told the Mirror. “As long as I can carry on doing what I do, I’ve no plans to retire.”

There’s no succession plan in place, Geffen said: Sir David Attenborough is irreplaceable.

“There is no new David Attenborough. You’ve got someone here who started in black and white, has gone through colour, HD, 3D, to where we are now, 4k and beyond. He spans the life of television in a way – he absolutely does, from the beginning. We’re never going to get someone who has done that span ... He’s a one-off.”