Rescued from a floating mattress in floodwaters in Sydney's west, Gerald the echidna is finally home and dry.

Locals discovered Gerald clinging to an old mattress that was floating downstream in flood waters at Pitt Town north-west of Sydney. His rescuer, James Pullan, took him home and called WIRES, which referred him to Taronga Zoo's Wildlife Hospital.

After spending two weeks recuperating in care, the echidna was released onto a wildlife reserve at Cattai on Thursday, March 31. It was a soggy day for Gerald's release but he dug into the dirt next to a new potential shelter - a hollowed-out log.

Taronga's Wildlife Hospital supervisor Liz Arthur said Gerald's case was "very special". Though the hospital doesn't normally do rescues, local WIRES volunteers had been cut off by flood waters, so the Taronga team drove out to collect Gerald themselves.

"He was swimming about in the river before he got onto the mattress so he was very waterlogged. His paws and beak were shrivelled up and pruny like when you get your hands wet for too long. He also had lacerations to his beak. But his body condition was very, very good," Ms Arthur said.

The team members tasked with Gerald's recuperation were concerned he might have inhaled or ingested toxic flood waters, so they did a full anaesthetic examination and checkup.

"We looked at his lungs to see if there was any evidence of water going in, but there wasn't. Echidnas are very good swimmers, and he'd obviously been swimming for a while. Because he was so strong and fit, that's why he survived and why he was able to grab a hold of that mattress," Ms Arthur said.

Mr Pullan, a Pitt Town resident, had been checking out the flood waters from his tinny when he happened upon the echidna.

"He was there on this mattress, floating down the river, so we thought we can't leave him, and we turned around and grabbed him, and got a hold of WIRES. I would never leave an animal behind. He was moving along quickly and I thought, if we don't pick him up, he could end up anywhere," Mr Pullan said.

"He looked scared and he had a lot of ants and spiders crawling on him - they were trying to get away from the flood with him."

It was Mr Pullan's 14-year-old daughter, Mikayla Pullan, who named him Gerald. "He just looked like a Gerald," she said.

Mr Pullan said it was "a lucky coincidence" that Gerald turned out to be male.

"He's become quite the celebrity - we never knew it would end up like this. There were four of us in the boat when we found him and we've all kept informed about how he is doing," Mr Pullan said.

"We're all very happy to see he's fine and he's going back into the bush and he'll live on. It's something nice to come out of something that's really terrible."