Officials in Marathon, Florida say the stingray jumped onto the boat as the woman was sunbathing Thursday morning.
Investigators are trying to figure out if she died from a blow to the head, a barb from the stingray or from a fall.
The stingray weighed about 75 pounds.
Officials say it's not unusual for stingrays to leap out of the water and into the air, but it is rare for them to collide with something.
