Rescue crews responded to a near drowning in waters fronting the Moana Surfrider around 10 a.m. Saturday.
According to EMS, lifeguards found the 58-year-old man floating face down. A jet ski operator pulled him to shore where he was revived.
The man suffered a cardiac arrest and was taken to the hospital in critical condition.
Officials say he is from Arizona and was participating in the Duke's OceanFest one-mile swim.
Event coordinators say in the 11 year history of the event, they've never had an emergency situation like this one.
With over 400 competitors, water rescue craft operators are always out on the ocean, monitoring all swim, surf, and paddle board contestants during the 9-day event.
OceanFest is held every year to honor Duke Kahanamoku.