Honolulu police say a 42-year-old woman drowned at Hanauma Bay on Sunday.
First responders got the call at around 10 a.m.
Officials say she was breathing when she was brought to shore, but later fell unconscious.
Ocean Safety officials performed CPR when a pulse could no longer be detected.
Police say the woman was pronounced dead in the afternoon. She has not yet been identified.
So far this year, five people have died while snorkeling at Hanauma Bay.