You will have to show your prowess as a swimmer, including freestyle, breast stroke, back stroke, and butterfly, as you will be expected to teach swim lessons. Not being great at one or more isn't a big deal as long as you show that you are coachable and willing to learn. You will be asked questions based on Red Cross lifeguard training and CPR/First Aid; it is important that you are comfortable with this and explain the reasoning for your answers. My interview was in person and between the questions and swimming it took around 1 hour.