Mystikins, have you tried those mineral makeups? Like Jane Iredale, or Bare Escentuals. I think they're supposed to be waterproof. They can be kind of expensive though. I've tried Jane Iredale, and it was okay, but it settle into the fine lines under my eyes.
Another is Clinique Almost Makeup. It's sheer, so you might need to dab concealer on a couple spots, but it is waterproof, and it also has SPF 15, which you'll need anyways. I've never tried it, but I hear its good.
I hope this helps, and I hope you have a fun summer!