An orca has died at SeaWorld, San Diego, after struggling for years with a bacterial infection. Kasatka is the third killer whale to have died at one of the SeaWorld parks in 2017.

"We are saddened to share the passing of Kasatka today," SeaWorld wrote in a post on their website, adding that the nearly 42-year-old orca's health had significantly declined in the day before her death, leading staff to decide to euthanise her.

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"Kasatka was the beloved matriarch of our orca family. A mother of four, grandmother of six and great grandmother of two, she was considered by the most current research as an older killer whale at nearly 42 years old." the parks said.

In late July, the last killer whale to be born in capitivity at the park died just three months after its historic birth. SeaWorld ended the breeding programme after intense pressure from campaigners.

SeaWorld came under heavy pressure after the documentary Blackfish criticised the practices of keeping captive orcas. The documentary followed the fortunes of Tilkum, a male orca implicated in the deaths of three individuals, who died in January.

"Nobody knows more about caring for killer whales than the professionals at SeaWorld," said Dan Ashe, President and CEO of the Association of Zoos and Aquariums in the post of SeaWorld's website. "Having the privilege of working with these animals daily provides veterinarians and other animal care staff with the expertise and insight to make very difficult choices, like with Kasatka."

Regarding the question about the decision to euthanise, the post says: "Kasatka's veterinarians and caretakers made the difficult decision to humanely euthanize her to prevent compromising her quality of life" and said that she had had a harder time "fending off the illness" as she had aged.

Kasatka had been diagnosed with the condition in 2008, the park said. Kasatka died surrounded by her pod, all of which "appear to be doing well" and were not threatened by Kasatka's infection, the park said.