From what I have heard, lifeguards do not have to be certified to apply. Disney will test your swimming skills and certify you themselves before you get hired. However, I would apply for sports and recreation if this is something you like to do. If for some reason you don't get accepted for the lifeguard role, recreation does watersports, beach and pool activities, boat rentals and much more. It would be a great way to introduce yourself to what Disney has to offer in that area.