NEW YORK (Reuters) - A three-month-old killer whale, the last orca to be born in captivity at a SeaWorld park, died on Monday (July 24) in San Antonio, Texas after suffering a possible pneumonia infection, the park said.

The calf, a female called Kyara, had been seriously ill over the past week and its condition worsened despite treatment from animal care and veterinary teams, said the park, owned by SeaWorld Entertainment Inc.

"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," SeaWorld said in a statement.

Kyara was born in April to a 25-year-old orca named Takara, who was already pregnant when the company said in 2016 that it was suspending its captive breeding programme and phasing out killer whale shows at its three parks in Orlando, Florida; San Diego, California; and San Antonio.

Attendance at SeaWorld theme parks has been falling amid bad publicity and criticism from animal rights activists upset by the treatment of captive marine mammals.

Colleen O'Brien, vice president of People for the Ethical Treatment of Animals (Peta), said on Monday that it was time for SeaWorld to release the 22 orcas still housed at parks to seaside sanctuaries.

"Forty orcas have now died at SeaWorld parks," she said in a statement after receiving news of Kyara's death. "SeaWorld has to move the remaining animals before the death toll hits 41."

SeaWorld officials said Kyara's pneumonia was not caused by being in captivity and the infection has been identified as one of the most common causes of illness in whales and dolphins, including those in the wild.

Other whales in the San Antonio orca pod were behaving normally on Monday and showed no signs of the illness, park officials said.