An endangered baby penguin named Holly has been reunited with its colony on Sydney's northern beaches after being saved from a stormwater drain in the city's inner west earlier this month.

The little penguin is weighed on scales at Taronga Wildlife Hospital. ( Supplied: Taronga Zoo )

The little penguin was rescued by the RSPCA at Haberfield and taken to the Taronga Wildlife Hospital where, suffering from dehydration and exhaustion, it was treated in intensive care for four days.

"This would have to be the strangest job I've ever had," Tyson Hohlein from the RSPCA said about the surprising encounter with the bird.

"Certainly I was a bit shocked to get the call for a penguin in Haberfield … I've been an inspector for two years."

The Taronga Wildlife Hospital's manager Libby Hall said the penguin "must have been very disorientated" at the time she was found.

"She just kept walking further and further up the drain, so yeah, she was lost," Ms Hall recalled.

'Every chance' Holly will survive

Hospital workers were delighted to see the juvenile penguin, who was just 10 weeks old, begin to recover.

Eighteen days after Holly was admitted to hospital, it was time to return the little penguin back to the ocean.

"We named her Holly because it's Christmas time and she's going home in time for Christmas," Ms Hall said.

Libby Hall is delighted Holly made a full recovery. ( Supplied: Taronga Zoo )

NSW Environment Minister Mark Speakman said this was a small but important step for the endangered colony.

"The Little Penguins of Manly are the last remaining penguin colony on the NSW mainland," he said.

Penguins in Sydney are threatened by dog and fox attacks, and are at risk from humans damaging their nesting sites.

But experts are confident Holly's adventures will continue for some time.

"She's a fantastic weight for a little penguin of that age," Ms Hall said.

"And so I'm just hoping that she'll survive, I think she's got every chance."