A two-year-old polar bear has died at the Assiniboine Park Zoo.

The zoo confirmed Sunday afternoon Eli the polar bear passed away Saturday.

Eli arrived at the zoo's polar bear conservation centre as a cub with his brother, York, in 2015 after their mother was accidentally hit by a cracker shell someone used to scare her and the cubs away from a building entrance in Churchill, Man.

Zoo officials declined an interview but said in a news release that Eli began showing "mild clinical symptoms" of illness on Friday before becoming more ill Saturday.

That's when zoo staff anesthetized him to find out what was wrong.

The bear died shortly after being given the anesthesia, the zoo said.

"We are all deeply saddened by Eli's passing. He was a part of our zoo family and this is a heartbreaking loss for our staff and visitors," said Gary Lunsford, senior director of animal care and conservation at the zoo.

The zoo said a preliminary necropsy, an autopsy for animals, has shown internal swelling of tissues in the bear's throat and neck. The swelling is believed to have interfered with his breathing and is the likely cause of death.

A full pathology report will be completed in the coming weeks after lab results are received and may provide more insight into the bear's death, the zoo said.

Zoo watchdog wants answers

Zoocheck Canada wants answers about how Eli died.

"Obviously we want to know what caused the bear's death, if there's some kind of toxin in the environment," said Julie Woodyer, campaign director for the national watchdog group.

"It's possible there was something in the environment that caused the animal's death."

Zoo officials are expected to provide more details about the death Monday morning.