Queensland shark attack victim was 23-year-old parks and wildlife worker Zach Robba

The Queensland ranger fatally mauled by a shark off the Great Barrier Reef has been identified.

Zach Robba was on the first week of his "dream job" when he was attacked off North West Island, 75 kilometres northeast of Gladstone, last night.

"This was Zach's dream job and he embraced all that it entailed," the Iona College Old Boys association said.

"Incredibly sad and lost for words, rest in peace mate," an alumnus wrote on the post.

Police say Mr Robba and the other rangers decided to go for a swim off the back of their boat, after spending the day doing maintenance work on the island.

Mr Robba's colleagues were ahead of him and had already reached the vessel when the shark struck.

"They would have witnessed the attack," Detective Senior Sergeant Tony Anderson told reporters today.

"There were four people swimming off the back of a boat, cooling down after a day's work."

It's not clear what kind of shark was involved.

Premier Annastacia Palaszczuk has paid tribute to the Queensland Parks and Wildlife Service officer, sending condolences to his grieving family.

"A lot of his work colleagues, I understand, were very upset today," she told reporters.

Mr Robba suffered extensive injuries to his leg and arm. He survived an emergency flight to the Gladstone hospital but later died.

The attack was the third near North West Island in just over three months.

In January, a nine-year-old girl was attacked by a shark, suffering a bite wound to the back of her leg, and puncture wounds to her foot.

A lemon shark was suspected of that attack.

And in late December a shovelnose shark bit a man in shallow waters at North West Island.

He suffered minor injuries to his right hand and leg.

There have also been a series of other shark attacks on the Great Barrier Reef over the past 18 months.

Last October two British backpackers were attacked while snorkelling at Hook Island in the Whitsunday Islands. One of the men lost his foot.

In March last year, a 25-year-old man suffered serious thigh injuries when a shark attacked him at Hardy Reef, near Hamilton island, which is also in the Whitsunday Islands chain.

Those attacks followed another fatality in November 2018, when Victorian doctor Daniel Christidis, 33, was killed at Cid Harbour at Whitsunday Island.