Judy Kay Zagorski, of Pigeon, Mich., was sitting in the front seat of a boat going 25 mph when the spotted eagle ray, with a wingspan of 5 to 6 feet, leaped out of the water, said Jorge Pino, spokesman for the Florida Fish and Wildlife Conservation Commission.
The 57-year-old woman's father was driving the boat on the Atlantic Ocean side of Vaca Key, Pino said.
"They do this all the time," he told CBS News' The Early Show. "They actually jump out of the water quite frequently, but I've never seen or heard of one jumping out of the water, colliding with a human being."
The family was only 500 yard from the shore, reports CBS News correspondent Kelly Cobiella.
"He had absolutely no warning. It just happened instantaneously," Pino said.
The collision knocked Zagorski backward onto the floor of the boat, Pino said.
The impact likely killed the woman, and she did not appear to have puncture wounds from the ray's barb, Pino said. An autopsy is planned, Pino said.
Zagorski's sister was standing next to her when the stingray appeared but was not injured, Pino said.
The stingray landed in the 25-foot boat and died from the impact, officials said.
Spotted eagle rays can weigh 500 pounds and have a wingspan of up to 10 feet. They are known to occasionally jump out of the water but are not aggressive. The rays do have a venomous barb at the end of their tail for defense.
Eagle Rays live close to the coast in depths of 3 to 60 feet and in exceptional cases they are found as deep as 900 feet, reports CBS News station WFOR-TV in Miami. It is most commonly seen along sandy beaches in very shallow waters.
The ray's two wings sometimes break the surface and giving the impression of two sharks traveling together.
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."
In 2006, a South Florida man was also critically injured when a stingray flopped into his boat and stung him. James Bertakis, 82, of Lighthouse Point, underwent surgery because the stingray left a foot-long barb in his heart. He has since recovered.
Pino advises vigilance to those who choose to boat in areas known to be inhabited with stingrays.
"If they know that there are stingrays in the area, the best thing is for them to slow down, be very cautious and be on the lookout because it could happen," he told The Early Show.