Fear of swimming

I went swimming today with my son at a local aquatic center. There is always an amount of trepidation on my part when I get in the water. Because water in my ears can really cause havoc. But with a pool full of children splashing around it can be very difficult. I've tried ear plugs but they usually fall out.
Worse than the fear of getting water in my ears is the disappointment in my son's face when I tell him that I can go under water and I can't go off the diving board. He is small ( seven years old) and tries to understand but sometimes he just can't. He sees other fathers jumping off the board and swimming underwater, why can't his father do the same thing? I know that this doesn't seem all that bad but it's just one of many things in my life affected by MM.