Some folks with MS in northern Texas have found that water aerobics allows them to exercise in ways they otherewise might not. The instructor tells us that "The physical benefits of the exercise help keep their symptoms under control."
i have to second this notion and tell anyone in decent shape who can get to a swimming pool to make a habit out of getting in and doing laps. it has a great effect on me. i can't say anything about long-term effect, but for 6-8 hours afterwards i feel great, symptoms are not troublesome.
get in the water