One of SeaWorld San Diego’s most prolific killer whales was euthanized Tuesday night after a long battle with a bacterial lung infection.

Kasatka was nearly 42 years old and had been treated for the condition since 2008.

“Kasatka’s health and appetite significantly declined over the past several days, despite continually tailored treatments,” said a statement released by SeaWorld. “Kasatka’s veterinarians, who are experts in marine animal medicine, and her caretakers made the difficult decision to humanely euthanize her to prevent compromising her quality of life.”

She was a mother of four, grandmother of six and great grandmother of two.

Kasatka is the third killer whale to die at SeaWorld parks this year. She passed just three weeks after the death of her granddaughter, 3-month-old Kyara at SeaWorld San Antonio.  Tilikum, the subject of the documentary Blackfish, died Jan. 6 of a bacterial lung infection at SeaWorld Orlando. He was estimated to be about 36 years old.

Killer whales have no natural predators and can live from 50 to 80 years of age, according to the National Oceanic and Atmospheric Administration.

Kasatka passed away at approximately 8:15 p.m. Tuesday surrounded by members of her pod, as well as SeaWorld veterinarians and caretakers.

The killer whale’s diagnosis was made following analysis of blood samples and through a bronchoscopy, which allowed veterinarians to obtain a culture from deep within her lungs nine years ago.

The 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. Kasatka received daily check-ups by her vets and treatments with a custom-built inhaler allowing the medicine to go directly to her lungs. Over the past year, as her immune system aged, it became more difficult for her to fend off the illness and her medication took longer to have an effect, according to the SeaWorld statement.

Kasatka was captured off the coast of Iceland in 1978, at less than two years of age. She was one of 11 orcas living at the SeaWorld San Diego Orca Encounter. Her condition was not contagious and the 10 other killer whales are being monitored by SeaWorld staff.

SeaWorld now cares for 21 orcas at its three facilities, including six in Orlando and five in San Antonio. Kasatka’s grandson Trua lives at SeaWorld Orlando.

SeaWorld’s veterinary team will conduct a post-mortem exam known as a necropsy to examine the extent of her illness and how it impacted her organ function.