The health of SeaWorld's killer whale Tilikum is deteriorating, the amusement park said, explaining that the aging whale has become increasingly lethargic.
Tilikum was the focus of the "Blackfish" documentary and has been connected to the deaths of three people.
He's now being treated for what veterinary and animal care teams believe is a bacterial infection in his lungs, but "the suspected bacteria is very resistant to treatment and a cure for his illness has not been found," SeaWorld said in a statement today.
The whale is receiving "the best care available" but "like all aging animals, he battles chronic health issues that are taking a greater toll as he ages," SeaWorld said.
"Veterinarians are focused on managing his illness in a way that makes him comfortable and creates an enriching life," SeaWorld said, explaining that his condition may continue to fluctuate.
"Since Tilikum became a part of SeaWorld’s family 23 years ago, he has received the best in marine mammal health care and life enrichment available for killer whales -- including a focus on his physical health, mental engagement and social activity with other whales," SeaWorld said.
SeaWorld says Tilikum is about 35 years old, which the park says is near the high end of the average life expectancy for male killer whales.
One of the deaths connected to Tilikum was in 2010, when the 12,000-pound, 22-foot animal pulled SeaWorld trainer Dawn Brancheau into the water and killed her.
The documentary "Blackfish" was released in 2013, examining how Tilikum and Brancheau arrived at that fateful moment. The documentary also raised the question of whether killer whales should be held in captivity.