Snorkelers near the Ahihi-Kinau Natural Area Reserve on the southwest coast of the island found the woman's body floating face-down in the water just before 9 a.m., and the injuries are consistent with a shark attack, Maui County government said in a statement.
The woman was only identified as a 65-year-old resident of Kihei, up the coast about 12 miles from where her body was found. Authorities said she was snorkeling with two friends when they became separated, and she was alone when the body was discovered.
Beaches and the ocean from the reserve to Makena State Park to the north, including a surf spot called "The Dumps" were closed until at least noon Thursday, the Department of Land and Natural Resources said.
There have only been two other shark attacks in all of Hawaii so far this year, according to the DLNR, which tracks shark attacks. Neither was fatal.
Until Wednesday, there had been only three confirmed fatal shark attacks in Hawaii waters since 1995, but all three of those occurred off the coast of Maui - two in the past 16 months, DLNR records said.
Comment: See also these other reports since the end of March:
Portents and signs: 5-legged lamb born in Wales
Portents and signs: Baby born with eight limbs in India
Portents and signs: Lamb born with face like an 'angry old man' in Dagestan