As far as salt water is concerned I have never heard of anyone having any issues with parasites. Fresh water that has little flow like small lakes can have dangerous parasites. These enter your system through your sinus’s and can be very dangerous. We have seen them in some of the small lakes in Florida. If I remember correctly the water temp. has to be pretty high for them to be a concern. I have read of several cases in the past couple of years but if I remember correctly all around August.