Relatives of a 43-year-old woman, who had been snorkeling at Sharks Cove, found her unconscious this afternoon.
Emergency Services Department spokeswoman Shayne Enright said in an email that the woman, a visitor from Washington state, got into trouble while snorkeling.
The surf was about 2 feet high. Bystanders started CPR until lifeguards arrived just after 12:30 p.m. today.
Emergency Medical Services personnel took over life-saving treatment and transported her by ambulance to an emergency room in critical condition.
The woman was wearing a full face mask.
Enright said no lifeguards are stationed at Sharks Cove, and urges the public to swim at lifeguarded beaches.
Of the four drownings on Oahu this year, three have occurred at beaches without lifeguards.