New images of the northern Great Barrier Reef have revealed more evidence of the long-term impact of this year's coral bleaching event.

It has been nearly four months since aerial and underwater surveys revealed bleaching had killed 35 per cent of coral in central and northern parts of the Great Barrier Reef.

The Climate Council's Tim Flannery was part of a team that has visited a popular offshore reef about 54 kilometres from Port Douglas.

"We wanted to see how much repair there'd been, but the coral we saw bleached and in danger a few months back has now mostly died," Professor Flannery said.

"On top of that we've seen a whole lot of new damage, a whole lot of white coral out there that's been killed by Crown of Thorns starfish because it was too weak to defend itself.

"I think it's going to take years to recover."

A new survey of the reef found more damage and coral killed by Crown of Thorns. ( Supplied: Climate Council )

Macquarie University's Lesley Hughes said the bleaching event had progressed past just bleached white reefs.

"Now you're not seeing so much really white coral," Professor Hughes said.

"What we're seeing now is that much of the bleached coral has died and it's started to be covered in algae. So there's green, brown sludgey algae on a lot of the corals."

Professor Hughes, who is also a Climate Council member, said the impacts on the rest of the environment, such as fish species, was clear too.

"The composition of the fish community has changed," she said.

"There's still a lot of fish that eat the algae and they're doing quite well. But fish like parrot fish, that eat the coral, have disappeared."

Coral that has not died from bleaching can recover, experts say. ( Supplied: Climate Council )

Coral that has not died from bleaching can recover, but severely bleached reefs can take more than a decade to return to their former condition.

Tourism operator John Rumney, who has been visiting the reef for 15 years, said he had also noticed a decrease in fish.

"I can tell you this reef was more than 100 per cent alive and now you go down there and in certain patches about 40 per cent is dead, in others about 20 per cent is dead," he said.

Mr Rumney said tourists were still visiting the reef.

"The experience is still fantastic, but tourists don't know what they're looking at. They don't know what it should look like," he said.

Other parts of the reef, especially southern sections, have not been as badly affected and are expected to recover.