
There is a hydrotherapy centre very close to where I live who do both health referrals and recreational swims. They are accredited by and a full member of the Canine Hydrotherapy Association and the owner - who works in the centre -holds the following qualifications :
(Copied from their website)
Introducation to Hydrotherapy
Canine First Aid (of which a refresher course / exam is taken every two years)
Canine Muscletal & Skeletal
Practices and Principles of Hydrotherapy
Conditions that benefit from Hydrotherapy
Understanding and Management of Arthritic conditions
Cruciate and Patella Disease Home Study Dissertation
Hip & Elbow Dysplasia Home Study Dissertation
Canine Aquatic Treadmill
Pool Water Management
They won't take any dogs - even those who wish to go purely for recreational purposes - where owners haven't obtained a letter from their dog's vet to say they are suitable to undertake hydrotherapy. My dogs are very well known to the owner as I used to belong to her agility training club and she knows they are very fit but I would still need to have a letter from my vet if I wished to book my dogs in for fun swimming sessions with her.
A friend used the facilities as a part of their fitness programme for one of her competing dogs - competes at the top level and her dog is very, very fast and had a clean bill of health. On reviewing the underwater film of her session it was apparent that one hind leg had a fair bit of restriction in it's movement whilst swimming - not noticeable at all when running or training. Armed with that knowledge she was referred to a specialist who diagnosed the onset of a problem that could have ended the dog's career without very early intervention.
With this in mind I personally would only use a hydrotherapy centre where the staff were fully trained and had extensive knowledge and a lot of experience with dogs.