Queanbeyan firefighters posted a video of the rescue on Facebook, showing deputy captain Bill Elder reaching down to pull the baby kangaroo out of the dam - finally succeeding after a number of failed attempts.

The Queanbeyan Rural Fire Service volunteers were part of the Lake George Brigade who had been sent to help battle the enormous Minnimbah bushfire, which has burnt more than 12000 hectares.

Queanbeyan resident and RFS volunteer Renee Smith said the team were patrolling the northern sector of the Minnimbah fire when they came across the old water source.

That's when she saw the kangaroo.

"He could jump but he couldn't get a grip on the concrete. He kept slipping back and it looked like he was in there for three hours," she said.

"He was totally drenched and he was very tired."

The firefighters tried to put in branches to help him get a grip, but the joey was too fatigued.

The video then shows them trying to get a lasso, made from rope in their fire truck, around the kangaroo's torso but that didn't succeed either.

Eventually, Ms Smith said, deputy captain Bill Elder got down on his stomach and pulled him out by the arm.

"We held him there for a bit to make sure he didn't have any life-threatening injuries," said Ms Smith. "[We] had called wildlife services to let them know and they were on standby but they weren’t needed."

The baby kangaroo wasn't the only wildlife the Queanbeyan crew encountered on their mission.

They also found rescued a possum from a burnt tree and helped an alpaca who had been tangled up in wire.

Ms Smith said their time on the front-line had become a bit of a wildlife rescue mission.

"It was very rewarding, we were all very happy with ourselves that... we were there to help the wildlife," she said.

Deputy captain Bill Elder said he was glad he could help. "It was a good thing," he said. "It felt good."