A racehorse named Rebel Rover has survived a two-kilometre swim out to sea after being spooked during a training session at a beach on Brisbane's bayside.

The five-year-old gelding with a track record of misbehaviour was being trained in chest-high water at Sandgate just before 9:00am yesterday when it was startled, tipped its rider and headed for deeper water.

Rebel Rover swam across Bramble Bay toward Redcliffe and was eventually rescued near Woody Point.

Volunteer Marine Rescue Brisbane spokesman Glen Philip said the 90-minute rescue operation was their most unusual callout for help, and a little like herding sheep.

"When we got to the horse he was in about four metres of water and he was swimming quite freely," he said.

"Luckily, we were able to manoeuvre our boat close to him and get a lasso around the top of his head which meant we could pull him nice and close to our boat and put a rope on its bridle."

Brisbane Water Police joined the operation, bringing the horse's jockey out to sea to help settle the animal.

He managed to jump on Rebel Rover's back and ride the horse out of the water.

'He was swimming a hell of a long time'

Rebel Rover heading for Redcliffe with Volunteer Marine Rescue in pursuit. ( Facebook: VMR Brisbane )

Rebel Rover's trainer Brad Smith said horses could swim, but did not normally do so very much.

"Any other horse, 20 minutes would probably see them out, but this horse — he must have a pretty amazing lung capacity," he said.

"The vet looked at him yesterday and again this morning and he's pretty well amazed with how he's coped with it all.

"[He's] a little bit tired and sore in the muscles because he was swimming for a hell of a long time, but he's quite remarkable for what he's been through."

Mr Smith described Rebel Rover as a character, saying its owners are now tipping big things.

"A couple of them told me he could probably run in the Melbourne Cup after that," he said.

He also said Rebel Rover had only recently returning to racing after a ban in Victoria for misbehaving in the barriers.

Rebel Rover is expected to resume racing next month.