I was in a hydrotherapy pool (at the hospital) with a cover on the wound the day after surgery and daily thereafter for my hospital stay. I was in the pool proper as soon as the wound was closed up and staples were out - about end of week 4 I think. (The docs would have been fine with me in a pool to continue hydrotherapy with a covered wound, but I would have had access to a private pool.) I started just walking in the water (backwards, forwards, sideways) and doing adductor, abductor and other movements against water resistance. I was swimming gently a week later, but no breaststroke, which it was recommended I should wait to start (I think until after 6 week doc check). Context: I am a swimmer, so very at home in the pool, and all of this was done in consultation with a PT working within the parameters set by the surgeon. Essentially, everything was gently progressive as I regained strength and ROM. I did the water stuff as well as (and part of) the walking and regular exercise rehab.
Hope some of this is helpful.