A 3-month-old killer whale named Kyara - the last orca born in captivity as part of SeaWorld's famous breeding program - died Monday at the San Antonio location.
The baby whale was being treated for an infection over the weekend, the Orlando-based company said.
"Kyara had faced some very serious and progressive health issues over the last week that the animal care and veterinary teams had been aggressively treating," the park said in a statement. "While the official cause of death will not be determined until the post-mortem exam is complete, we know that Kyara had an infection, likely pneumonia, and that her health continued to decline."
Kyara was born in April to a whale named Takara
"The team's attention now turns to the rest of the orca pod, especially Takara, to provide the care and attention they need," SeaWorld said.
For more details, see SeaWorld's statement on the baby orca.
SeaWorld has not taken in any wild orca for almost four decades. Most of its current animals were born in captivity.
After pressure from animal rights protests - and backlash after a trainer was killed and others injured by some of the whales - SeaWorld announced in 2016 it would be ending its orca breeding program.