I have a fit healthy dog who needs to develop some muscle to fill him out ! I 'm afraid I cant let him off the lead as he has a habit of doing a disappearing act, so hydrotherapy has been suggested, and I have found somewhere local to take him.
What I am looking for is a little bit of advice so I am not going into this blind, are there any guidelines for how long he should swim for to start with, and how he should then progress?

This link might help as well as this one

Many years ago before the dog hydropools were built I used to take my BC with severe HD to a local horse trainer who had a horse pool. My dog was already a good swimmer & we used to swim him against the flow of water on a lunging line & nylon harness

Todays pools are much better & have driers floatation aids etc