Two Calgary Zoo employees have been disciplined for giving an otter a pair of pants, leading to its death.

The pants were given to the animal as an "unauthorized enrichment item," according to zoo officials.

The otter became tangled in the clothing and then drowned, according to a necropsy.

"This error is simply unacceptable," zoo curator Colleen Baird said in a news release.

"Our animal care protocols are among the most stringent in the industry and must be followed. We will be reinforcing our protocols with every member of our animal care staff to prevent an incident like this from ever happening again."

The male river otter, named Logan, was seen struggling in the pool last week.

A zookeeper jumped into the pool to its aid, but the 12-year-old animal did not survive.

When asked, Baird refused to say what type of discipline the two employees face, but said neither was fired.

"Sadly, there was a mistake that was made — human error — and an unauthorized piece of enrichment was in there and an otter died because of it," she told CBC News.

A Toronto-based animal protection organization says using pants as an enrichment item is irresponsible.

"It smacks of the kinds of things you might see at a roadside zoo, not in a professional operation," said Julie Woodyer of Zoocheck.

The otter's death is not the first to occur at the Calgary Zoo under unusual circumstances.

In 2013, a female penguin named Fiona died in what was described as a freak accident, after it swallowed a nearly foot-long stick that ended up its open-air exhibit area. The stick was surgically removed, but the penguin died of internal bleeding eight days later.

In 2012, two zoo employees were disciplined after a great grey owl was killed while being transported from one area to another. The bird was fatally injured after it got loose and flew into a gate, which the zoo blamed on a lack of planning and lack of radio communication between the employees.

In 2009, an employee was suspended for two days after crushing a female capybara in a hydraulic door. The zoo said the staffer was moving the exotic rodent from one enclosure to another and not following proper protocol when the mishap occurred.

In 2008, nearly all of the cownose stingrays in a newly opened exhibit suddenly died, with 41 of 43 of the animals perishing. Nearly a year later, the zoo concluded with "99.9 per cent" certainty that a lack of oxygen in the water was responsible for their deaths.

In 1999, the zoo closed what was at the time a controversial polar bear exhibit after one of the Arctic animals died. The polar bear, named Misty, had been prescribed the anti-depressant drug Prozac to control its erratic behaviour.

The numerous high-profile deaths prompted the zoo to undertake an external audit of its operations and the results, released in 2010, revealed numerous other animal fatalities that were less publicized, including:

A spider monkey was fatally crushed by a hydraulic door.

Another spider monkey died from frostbite complications after it was left outside in cold weather.

Four feather-tailed sugar gliders — mouse-like mammals — were either crushed to death underfoot or by a door.

Several mule deer were killed or injured while handlers tried to capture them for veterinary checks.

Dozens of Sebas and Pallas bats died after hitting piano wire strung across their cages as part of their exhibit.

Knife-wielding gorilla

One of the most high-profile mishaps at the Calgary Zoo, however, was a non-fatal one.

In 2009, a gorilla keeper inadvertently left a knife in the animals' enclosure, which one of the gorillas picked up and played with, appearing at times to brandish the weapon menacingly.

Barika, a gorilla at the Calgary Zoo, holds a knife accidentally left behind by a zookeeper in this photo taken in June 2009. (Heike Scheffler)

The bizarre scene was photographed by a zoo visitor and made international headlines.

The zoo later described the incident as being "overblown" and noted that, despite the appearance of the photos, gorillas don't understand the concept of using tools as weapons.