Kasatka the killer whale performs during SeaWorld’s Shamu show Nov. 30, 2006, in San Diego. (Chris Park/AP)

Veterinarians at SeaWorld San Diego have euthanized the matriarch of its killer whale clan following a battle with lung disease.

Marine park officials said Kasatka, who was nearly 42 years old, died late Tuesday “surrounded by members of her pod, as well as the veterinarians and caretakers who loved her.” The killer whale had not been responding to treatment for a bacterial respiratory infection, and caretakers decided to euthanize her “to prevent compromising her quality of life,” the park said earlier this week in a statement.

“I have spent the past several years with Kasatka and was truly blessed to be part of her life,” orca behaviorist Kristi Burtis said.

“Although I am heartbroken, I am grateful for the special time we had together and for the difference she has made for wild orcas by all that we have learned from her. I adored Kasatka and loved sharing her with millions of people. I will miss her very much.”

Kasatka was diagnosed with a lung condition in 2008, and caretakers had tailored a treatment plan for her, which included a custom-made inhaler that pumped medicine into her lungs, SeaWorld said.

“Kasatka was being treated for a respiratory bacterial infection, or lung disease, for several years but as she aged she had a more difficult time fending off the illness,” the marine park said Tuesday in the statement. “Kasatka had a dedicated team of veterinarians and care staff providing critical care. Despite their best efforts, her health and appetite significantly declined over the past several days despite continually tailored treatments.”

Kasatka became the third orca to die at a SeaWorld park this year.

In January, Tilikum, the well-known killer whale that killed a SeaWorld trainer, also died after a battle with a lung infection.

And in July, Kyara, a 3-month-old orca that was the last born in captivity under SeaWorld’s now-defunct orca-breeding program, died after suffering what veterinarians believed was pneumonia.

Following Kasatka’s death, SeaWorld said, “This type of respiratory condition has been identified as the most common cause of mortality and illness in whales and dolphins, both in the wild and in zoological facilities.”

SeaWorld has been under intense scrutiny since the 2013 documentary “Blackfish” suggested that the marine park’s treatment of killer whales has prompted some gruesome attacks. It evoked calls for change from animal rights advocates, corporations and lawmakers. It has moved lawmakers to attempt to ban orca captivity, companies to pull out of partnerships and researchers to study large ocean animals.

The embattled marine park announced last year it was ending its controversial captive-breeding program for orcas.

“Why the big news?” the company said in a statement at the time. “SeaWorld has been listening and we’re changing. Society is changing and we’re changing with it. SeaWorld is finding new ways to continue to deliver on our purpose to inspire all our guests to take action to protect wild animals and wild places.”

Kasatka was not born in captivity; but was captured in 1978 in Icelandic waters, according to the Associated Press.

Years later, Kasatka, too, was involved in an attack at SeaWorld. As The Washington Post’s Michael E. Miller reported, the killer whale bit her trainer’s foot during a trick, then dove deep into the water, pulling him along.

The trainer, Ken Peters, fought for air for more than eight minutes before Kasatka finally let him go.

On Wednesday, People for the Ethical Treatment of Animals decried the killer whale’s life in captivity and recent death.

PETA Executive Vice President Tracy Reiman said in a statement that SeaWorld “didn’t even respect this orca enough to give her a good-quality life, and it needs to send the remaining marine mammals to seaside sanctuaries before they follow Kasatka — and the 40 orcas before her — to the grave.”

Kasatka had two daughters and two sons, six grandchildren and two great grandchildren, SeaWorld said in a statement.

SeaWorld currently has 21 orcas at its three marine parks in Orlando, San Antonio and San Diego.

Read more:

A mob of beachgoers wanted to play with a baby dolphin — and wound up killing it

A rare and elusive white moose has finally been captured on video

This ‘pink’ dolphin makes waves whenever it’s spotted