Depending on your insurance coverages, some docs will prescribe you a therapeutic pool prescription. Then you go and buy a continuous pool,(the ones that make a current to swim into). Insurance may or may not cover most to all the cost.(check with them on the coverage for it).
They make a great way to relax in the hot summer months too.
Jerry swimming cant be beat on a work out. No impact, and it works every muscle group in your body.