Practically none, I was hired on the spot. Asked me a few questions about availability. Couldn't answer my questions about the job and it was very vague. They needed lifeguards at the time so they let me pick a park at the interview also. You must pass the lifeguard test though

It was a group interview with about 15 other people. They split us into two groups and had us perform little activities together. It was kind of fun and a lot less stressful than a 1 on 1 interview. Once I received the job offer, I got the date and time for my swim test. If you know how to swim and breathe properly while swimming, you'll do fine on the swim test.