Kurt - I'm a great fan of swimming. I've always been good at it, state level in high school, blah blah blah. Excellent workout, and I enjoy the solitude and challenge it brings me. It's low impact, too, so it may be ideal for you.
I haven't been in a while, though. Methinks I should get wet (maybe back to three or four times a week?).
Let us know how it goes for you.