Officials say Nala, the Vancouver Aquarium's youngest beluga whale, likely died when her airway was obstructed by inflammation from foreign objects lodged in a unique pocket branching off from her airway.

Aquarium veterinarian Dr. Martin Haulena said the calf first showed signs of illness two weeks ago, but had been responding well to medication until her condition suddenly deteriorated on Monday. She died that night at 10:15.

"The loss was sudden and unexpected," Haulena said. "It's hugely sad, all of us care very deeply about the animals. A one-year-old calf is one of the most precious things you can imagine working with."

A full necropsy was conducted overnight, which found two rocks and a penny caught in a unique pocket in the whale's airway. The pocket was inflamed, blocking the airway, and fluid had accumulated in her lungs.

"This was unforeseeable. At this time we are unsure if the airway pocket, which has not been previously seen in the examination of other belugas, was congenital. We will be investigating further.