Oh that's kind of crazy to hear because I'm the same way, but I worry about having some type of water weed at the bottom wrap around my legs so that I can't get back up for air and I drown. I also worry about dead bodies decaying in the bottom of the lake, or touching a corpse with my foot. I know that's really stupid, but... Part of my fear is not being able to see the bottom in a body of water. When I can see the bottom, I feel safe. However those weird fears don't actually prevent me from swimming in lakes or oceans, I still swim in them, but I'd much rather be in a nice, safe pool.
hmmm... they are your kids... if they've been invited, you're the mother, you should have just as much right to go.
How 'bout obtaining a kiddie pool, & a sprinkler to run around under for your place? Not the same as going swimming, but could make for some enjoyable lounging in hot weather anyhow.