A lifeguard...
Is a person who supervises the safety and rescue of swimmers,
surfers, and other water sports participants such as in a swimming
pool, water park, or beach. Lifeguards are strong swimmers and
trained in CPR/AED first aid, certified in water rescue using a variety
of aids and equipment depending on requirements of their particular
venue. In some areas, lifeguards are part of the emergency services
system to incidents and in some communities, the lifeguard service
also carries out mountain rescues, or may function as the primary
EMS provider.