Assiniboine Park Zoo announced Sunday that one of its polar bears passed away on Saturday.

The bear, which was nearly three-years-old, had been at the zoo since November 2015.

In a release, the zoo said the bear, named Eli, began showing mild clinical symptoms on Friday and was given treatment from vets. His condition got worse on Saturday and the zoo decided to anesthetize the bear to determine the cause of its illness.

Eli passed away shortly after being anesthetized, the zoo said.

“We are deeply saddened by Eli’s passing. He was part of our zoo family and this is a heartbreaking loss for our staff and visitors,” said Gary Lunsford, the senior director of animal care & conservation at Assiniboine Park Zoo, in the release.

Zoo staff performed a necropsy, which is an animal autopsy, on Eli’s body and discovered internal swelling of tissues in his throat and neck. Staff believe the swelling interfered with his breathing and is the likely cause of death.

There is no concern for other animals, the zoo said.

Eli was named in honour of an elder from a northern First Nation and arrived with his brother York.

The two cubs were transferred from Churchill when they were about 11 months old, orphaned after their mother was accidentally shot.

The zoo said polar bears need to stay with their mother for at least the first two winters and many wildlife experts believe cubs as young as Eli and York would not survive on their own.

On Sunday, visitors at the zoo were shocked and saddened to learn about the young polar bear's death.

"It's wonderful that we can come and see the polar bears and experience what's happening in the arctic. It's really sad news,” said Darius Mirza.

"I'm pretty shocked,” said Corinna Wolke.  It's very saddening because I bring my kids here every year, because the polar bears are the main attraction here."