MARATHON, Fla. - A 34-kilogram stingray killed a Michigan woman Thursday when it flew out of the water and struck her in the face as she rode in a boat in the Florida Keys, officials said.

Judy Kay Zagorski, 57, of Pigeon, Mich., was sitting in a boat going 40 km/h when the spotted eagle ray, with a wingspan of 1 1/2 to two metres, leaped out of the water, said Jorge Pino, spokesman for the Florida Fish and Wildlife Conservation Commission.

The woman's father was driving the boat on the Atlantic Ocean side of Vaca Key, Pino said.

"He had absolutely no warning. It just happened instantaneously,'' Pino said.

The impact likely killed the woman, but it was not immediately clear if she had any puncture wounds from the ray's barb, Pino said. An autopsy will determine an official cause of death, Pino said.

Spotted eagle rays can weigh up to 225 kilograms and have a wingspan of up to three metres. They are known to occasionally jump out of the water but are not aggressive and usually use the venomous barb at the end of their tail as a defence mechanism.

The rays are protected in Florida waters and are typically seen swimming on the water's surface.

"Rays jump to escape a predator, give birth and shake off parasites,'' said Lynn Gear, supervisor of fishes and reptiles at Theater of the Sea in Islamorada. "They do not attack people.''