Just emailing the manager or the club. It is very casual and it helps if you know friends who work there who can refer you to the management. The manager is friends with the local high school swim team coaches, so if you're on the swim team, you can ask your coaches about it. There is no personal interview process or anything formal really. They do ask that you list two references that they will contact briefly. Otherwise, if you have an unexpired deep pool lifeguard+AED certification, you're good to go.