From CNN:

 A killer whale killed a trainer Wednesday afternoon at SeaWorld’s Shamu Stadium in Orlando, Florida, a public information officer for the Orange County Sheriff’s Office said.

The 40-year-old woman, identified by sheriff’s spokesman Jim Solomons as Dawn Brancheau, was in the whale holding area about 2 p.m. when "she apparently slipped or fell into the tank and was fatally injured by one of the whales," he said.

But a witness told CNN affiliate WKMG-TV that the whale approached the glass side of the 35-foot-deep tank at Shamu Stadium, jumped up and grabbed the trainer by the waist, shaking her so violently that her shoe came off.

From ClickOrlando.com:

Jim Solomons of the Orange County Sheriff’s Office said she fell into the tank and, "this appears to be an accidental death."

"It is with great sadness that I report one of our most experienced trainers has drowned in an incident with one of our whales this afternoon," park manager Dan Brown said.

Brancheau had 16 years experience working with killer whales, the sheriff’s office said.

The park was closed because of the fatal incident, and the Sheriff’s Office is conducting a death investigation at the theme park.

"We have never in the history of our parks experienced an incident like this and all of our standard operating procedures will be under review," Brown said.

Witness Victoria Biniak said she saw the deadly incident from a viewing area.

"The trainer was explaining different things about the whale and then the trainer that was down there walked away from the window. Then Telly (the whale) took off really fast in the tank and he came back, shot up in the air, grabbed the trainer by the waist and started thrashing (her) around," Biniak said. "He was thrashing her around pretty good. It was violent."

Biniak said the attack was so violent that it caused the trainer’s shoe to fly off.

"He was thrashing her around pretty good. It was violent," Briniak said.