Okay, I'm going to chime in here (puts on optometrist hat)...

You should NOT swim in contact lenses. My recommendation would be for someone who does a lot of swimming to get prescription goggles. Okay, I know that isn't always practical (especially for tris when you need to bike/run after) so if you HAVE to wear your contacts I'd get some daily disposables that you can chuck immediately after the event. Also, be sure to wear goggles to minimize the contact with the water.

Water (especially fresh water, hot tubs, pools) has a lot of nasty bugs in it that can get into your contacts and cause really, really bad eye infections. I emphasize the REALLY BAD part of that statement.

Kelownagirl, if you'd just had PRK and the front of your cornea hasn't fully healed yet, you might have little abrasions on your cornea which are portals of entry for these bugs. I'd call your eye doc up and be honest that you have this event and would like to wear CL's during the swim. See what he says. Maybe your eyes are healed enough that he'd reluctantly agree for a one time deal (get a pair of daily disposables). Maybe your eyes aren't healed enough and he's the one who would know.