The Maine Department of Marine Resources on Tuesday identified the woman as 63-year-old Julie Dimperio Holowach, of New York City, who was attacked by a great white shark near Bailey Island.
"I want to first express my condolences to Julie's friends and family, and to thank the individuals who responded and help bring this situation to a closure," Commissioner Patrick Keliher said. "We urge swimmers and others recreating in or on the water in the Casco Bay region, and in particular near Bailey Island, to be aware of their surroundings and to avoid schools of fish or seals, which attract sharks."
WATCH: Maine officials discuss deadly shark attack
Maine Marine Patrol said a witness saw the woman swimming about 20 yards from shore when she was injured in what appeared to be a shark attack just before 3:30 p.m.
Two kayakers helped Holowach get to shore and an ambulance provided further assistance, but she was pronounced dead at the scene.
There has only been one recorded unprovoked shark attack in Maine, which occurred 10 years ago near Eastport and involved a porbeagle shark.
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Sulikowski, who researches for Arizona State University, said it's possible the shark mistook the person for food.
The rescuers were a man and woman in a rented tandem kayak, said Jeff Cooper, co-owner H2Outfitters on the island, which offers instruction, rentals and sales of kayaks.
The kayakers were on the shore when one of them saw something breach, and realized something was wrong, Cooper said.
"They happened to be right there at the scene. They were courageous enough to jump in and retrieve the victim," Cooper said.
One of the kayakers grabbed Holowach, and the other paddled to get her back to shore, said Cathy Piffath, the other co-owner. The kayakers asked not to be identified.
Holowach and her family own property in the area and are well known in the community, which is shaken by her death, said Rob Beal, major of the Maine Marine Patrol.
Large sharks prey on seals, which are common off Maine. Two coastal state parks, Popham and Reid, are not allowing swimmers beyond waist deep water, state officials said.
Bailey Island is part of the town of Harpswell, about 40 miles up the Maine coast from Portland. Harpswell is a town of about 4,700 that is popular with vacationers and second homeowners for its coast, beaches and sweeping views of Casco Bay.
The Associated Press contributed to this story.