The death happened at the Calgary Zoo in Canada.
An investigation into the death of 12-year-old Logan revealed that a zookeeper gave the pair of pants to the otter as an “unauthorized enrichment item.”
The zookeeper and another staff member found to have broken zoo protocols were disciplined.
“This error is simply unacceptable,” said Colleen Baird, the zoo’s general curator, in a statement.
“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.”
Critics said the situation was the kind you’d usually find at less established places.
“It smacks of the kinds of things you might see at a roadside zoo, not in a professional operation,” Julie Woodyer, from animal welfare group Zoocheck, told CBC.
The discipline the employees were given was not detailed.
The death is just the latest in a string of incidents at Calgary Zoo, with a female penguin dying after swallowing a stick in 2013, and a great grey owl dying after it got loose and flew into a gate in 2012, among others.