I used to work at a private rescue with a small outdoor pool (not as posh as it sounds!!) I have seen amazing changes in dogs after hydrotherapy an some not quite so good. Some years ago a rescue lurcher we had needed a cruciate repair, a risky operation due to her appalling treatment before us and the resulting health issues. Once her stitches were out I carried her to the car then down to the sea everyday. I waded out to my waist (it was summer thankfully!!) with her on a harness, placed her in the water, pointed her at the shore and held on Our vets were amazed at her progress considering all that was stacked against her and she went on to enjoy several more years of four legged activity I would say that it is not cheap and you may find you are many miles away from your nearest centre (as was the case with us) I would discuss it with your vet and see what they have to say.
We took our lovely elderly greyhound bitch to hydro as part of the management of her arthritis. We did it after a lot of discussion with the vet, and with their encouragement. Initially, she went once weekly and after an initial intensive phase, reduced her frequency to a maintenance programme of visiting fortnightly. We think it gave her an extra year of good quality of life and mobility - she passed away a year ago this week of an unrelated problem, age 13.
I would have no hesitation in recommending it, especially if your vet has suggested it.
We had an excellent therapist - very thorough, very professional and very gentle with our dog. She was not a water loving dog before her treatment but used to really enjoy going.
It is expensive, as insurance did not cover us since her arthritis was a pre-existing condition, but your policy might cover you. In any case, we think it was worth every penny.
The floating treadmill may well work then they fill it to chest height the dogs wear a life jacket so are supported in the water. It promotes the correct muscles for walking which swimming does not. I have a patient who had a prolapsed disc currently having this treatment after a hemilaminectomy surgery.