Kiska, who was captured in Icelandic waters in 1979, was around 47 years old.
Kiska, the last captive killer whale in Canada, has died, the Ontario government said late on Friday, adding it was informed of the death by the theme park where Kiska lived.
"The ministry was advised by MarineLand that the whale named Kiska passed away at MarineLand on March 9, 2023. A necropsy was conducted by professionals retained by MarineLand," Brent Ross, a spokesperson of the Canadian province's solicitor general ministry, said in an emailed statement.
MarineLand is a theme park in Niagara Falls, Ontario. Kiska, who was captured in Icelandic waters in 1979, was around 47 years old.
MarineLand said Kiska's health had declined in recent weeks.
"Marine mammal care team and experts did everything possible to support Kiska's comfort and will mourn her loss," local media quoted the theme park as saying.
Canadian non-profit group Animal Justice, which advocates for animal rights, called for a probe into MarineLand's treatment of the killer whale.
Animal rights group People for the Ethical Treatment of Animals (PETA) described Kiska as the "world's loneliest orca" whose life was marked by "tragedy after tragedy" after all five of her calves died before they were seven years old.
"Animal Welfare Services was onsite to determine compliance with the Standards of Care," Ross said. MarineLand has been inspected 160 times since January 2020 as part of Animal Welfare Services' work to ensure the standards of care are being met under the law, Ross added.