Leigh Shepherd said they found their neighbor's 25-year-old horse, Tilly, struggling in deep water in front of their home on Friday night after his wife heard a noise from the yard.
Mr Shepherd swam out to the horse after his wife declared she was going to get it.
"I couldn't stand all my friends saying 'you let your wife swim out into flood waters, what were you doing?' So obviously I had to go out and get the bloody thing," he said.
It took several attempts to get the horse to safety, culminating in his son Rob getting an extension cord and using that to lead the horse to a stairwell outside their house.
The horse made it up the stairs and onto the landing, though still in water.
"Once she got up there she was exhausted and she just collapsed," Leigh Shepherd said.
Rob Shepherd, 21, held Tilly's head above water on a boogie board for more than five hours waiting for the water to recede.
"She was just buggered, she couldn't move, she just lay there and was dependent on us," he said.
"We thought if she wasn't going to drown maybe hypothermia or something like that would have got her."
Tilly's fight convinced rescuers to keep helping her out
Leigh Shepherd said there were several times through the night when the horse looked close to death and they were concerned about what they would do if she died in their doorway.
"There was one time there where we actually took the boogie board out and she struggled to keep her head above water," he said.
"And we thought 'she wants to live', so we just kept it under there and we're so happy we did."
Equine veterinarian Greg Baldwin treated Tilly over the weekend for a number of minor injuries.
"Remarkably she has come through it pretty well," he said.
|Neighbors posted online, trying to track down her owners|
"She has a reasonably severe wound on her forehead, a few scratches and bruises, a couple of rubs on her hip, but she's come through it."
The Murwillumbah-based veterinarian said it was particularly heartwarming to hear about the effort the Shepherd family made to keep the horse alive.
"The guys basically had no horse knowledge, they just did the best they could in a situation that was a disaster zone really," he said.
"The owners are very grateful for the boys. They did their best.
"Murwillumbah is reeling at the moment; there is a lot of devastation and a lot of damage and people lost not only their businesses, but their houses.
Tilly has since been reunited with her family and best friend, a pig called Snooky.
|Tilly back home with her best friend Snooky|
(Australia Broadcasting Network - April 2, 2017)