A wayward wallaby has had a lucky escape, being plucked from Sydney Harbour by workers on a ferry.

The struggling marsupial was spotted swimming desperately about 50 metres from shore near Manly yesterday evening, before it was rescued.

It is the second wallaby to be spotted out of its comfort zone in Sydney this year. Police caught one going for an early morning bounce along the Harbour Bridge in January.

During last night's incident, workers looped a rope around the animal and pulled it aboard about 7.15pm, delaying ferries.

Joseph Battaglia is a volunteer with the Sydney Wildlife rescue group who was working with fairy penguins nearby when a bystander raised the alarm about the wallaby.

"This woman came to us with a pram and a couple of kids in it and said a wallaby has just jumped into the water around at Fairlight and is swimming across," he said.

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He said wildlife rescue volunteers rushed up on to the wharf and spotted the wallaby swimming in the water, where it got in front of a ferry.

Manly Fast Ferries crew members Chris Thomas (L) and Jason Campbell (R) rescued the wallaby. ( ABC News: Karl Hoerr )

A Manly Ferry staff member then threw a life ring at the wallaby without success.

Ferry worker Chris Thomas can be seen in footage using a rope to haul the wallaby out of the water.

"What they did was they put a rope around the front of the wallaby in the water and then they used a boat hook to grab hold of its tail ... and they managed to raise it onboard the boat, the Manly Fast Ferry," he said.

Mr Battaglia then jumped on board the ferry and helped calm the wallaby, before taking it to a vet to be checked.

A rope was used to pull the struggling wallaby out of the water. ( Facebook )

Jackie Carroll from Sydney Ferries said a crowd was watching from the wharf.

Eira Battaglia, Joseph Battaglia and Sue Matthews are wildlife volunteers who happened to be nearby to help the wallaby. ( ABC News: Antonette Collins )

"There were people watching, staff on [the] wharf were watching and then later assisted — a staff member threw a towel on it once they rescued it," she said.

"The wallaby was exhausted when they got it on board, so one of the staff was holding it and calming it down."

Ms Carroll said the priority was to get the animal out of the path of other ferries and boats.

"Luckily we had three crew on board at that time; one person was driving the boat and one was leaning over the side while another staff member had the rope," she said.

"The staff member who was leaning over had his legs held down so he didn't slide off.

"He was lying on the deck leaning quite far over to save the wallaby."

The wallaby was discovered to be young female which has now been nicknamed Chrissy after Mr Thomas, the ferry worker who pulled the animal to safety.

During the January 16 incident, a young swamp wallaby was spotted on the Harbour Bridge just before 5am.

NSW Police followed the animal, and eventually caught it on the Cahill Expressway near the Conservatorium of Music.