Another animal at Assiniboine Park Zoo has died. One of its harbour seals in the Journey to Churchill exhibit drowned after getting caught in an underwater drain.

“We don't know exactly what happened. We don't know. They do explore. They look around and perhaps he was investigating the water flowing out of the pool and got stuck. We just will never know,” said Dr. Brian Joseph, director of zoological operations.

The seals can hold their breath for up to 20 minutes.

“This is something we didn't anticipate. We've taken corrective action. We don't use that drain line anymore, so it can't happen again,” said Joseph.

The animal, named Caelum, drowned in an area not visible by casual observers and it happened at some point over night when the public wasn’t around.

Zoocheck Canada said it never should have happened.

“Let's face it - in the pool environment there are very few hazards that can cause the death of an animal,” said Julie Woodyer from Zoocheck Canada.

She said she’s especially concerned in light of other recent events at the zoo.

Nearly two months ago, a tiger was mauled to death by another tiger at the zoo after a zookeeper accidentally left a gate open.

Earlier that month, the zoo was forced to shut down the polar bears underwater enclosure after learning they were chewing the sealant. In July, the zoo learned their wolves were trying to tunnel into the polar bear exhibit.

Zoocheck Canada said it’s more than just a run of bad luck.

"It's probably a sign that there are systemic problems within the zoo,” said Woodyer.

The zoo, however, said that’s not the case.

"These are all coincidental new events. Certainly, when you have a new facility that's complex, you expect things like caulking and digging, but, no, we don't see them related at all," said Joseph.

The zoo emphasized staff and volunteers are saddened by the death of the seal and have taken steps to ensure nothing else can happen to the other seal, Neptune.

Joseph said the zoo constantly does risk assessments on the entire operation, including the area where the seals were housed.

The animal who died was one of two blind rescued harbour seals transferred in the summer from the Vancouver Aquarium to the Assiniboine Park Zoo.