Heidi, a four-year-old continental giant rabbit, from Dorset has had sessions in a heated pool while wearing a life -jacket.
Hydrotherapy pool owner Linda Prove said she was sceptical when a vet referred the rabbit, but the treatment was "working incredibly well".
Heidi's owner Amanda Williams, from Christchurch, told the BBC that her pet took to it like a "duck to water".
Heidi, who weighs about 7kg, had been diagnosed with arthritis in her hips and knees and spondylosis in her neck.
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While rabbits can swim in the wild, Heidi wears a buoyancy jacket during the sessions and is carefully dried afterwards to prevent hypothermia.
Williams said: "None of us thought she would tolerate even one minute in water.
"She is certainly a lot more lively and is obviously benefiting from this treatment.