Swimming with Parkinson's Disease

I did a search of the forums and couldn't find this topic being discussed anywhere. But I am curious if any of our members who have been diagnosed with PD and continue to swim might share any tips or advice with regards to training. Two friends of mine here in the Pittsburgh area have recently been diagnosed, and both are determined to continue swimming despite slowing down. It seems to me that aquatic exercise could be a great way to exercise and perhaps even slow down the progression of the disease. Surely, there must be within the greater USMS ranks more than a handful of swimmers who are currently contending with this disease. I told my one friend, who isn't a USMS member, that I would post an inquiry on his behalf here on the forums and share any results it might turn up. Thanks in advance!