BROOKFIELD, Ill. -- Four southern stingrays and 50 cownose rays died at Brookfield Zoo after a malfunction caused oxygen levels in their habitat to drop, officials said.
Although the levels were returned to normal by on-scene veterinary and animal care staff following the incident, which occurred on July 10, the animals died as a result.
"We are devastated by the tragic loss of these animals," said Bill Zeigler, senior vice president of animal programs for the Chicago Zoological Society, in a statement. "Our staff did everything possible to try and save the animals, but the situation could not be reversed."
Officials say staff members are investigating the cause of the malfunction.
54 rays die after malfunction at Illinois zoo