Fripp Island has a wonderful stretch of a beach for walking along the salty Atlantic Ocean. Keep your walks there and keep up with airway clearance and I suspect you'll be fine. It seems to me the key is not to let the secretions in your lungs pool.

I believe Dr. Falkinham on the NTMinfo.org site weighed in on marshes. Perhaps check that site to read Dr F's exact words. I seem to recall he said the increased risk is related to aerosolization of water droplets. So, unless there are waterfalls and rushing water walking along marshes is not the riskiest thing you could do.