Dawn Brancheau, 40, was explaining details of a frequently performed show at Shamu Stadium at 2 p.m. when the 12,000-pound male whale named Tilikum pulled her into the tank, where she drowned.
About two dozen tourists witnessed the attack from above the tank and from an underwater viewing area, according to the Orlando Sentinel.
Witnesses said the whale had grabbed Brancheau by the upper arm or waist. "He was thrashing her around pretty good," Victoria Biniak tells WKMG-TV. "It was violent."
Paramedics were called to the theme park but could not revive the woman, who was pronounced dead at the scene.
"It is with great sadness that I report one of our most experienced trainers has drowned in an incident with one of our whales," park manager Dan Brown says, according to the WKMG.