GRAND RAPIDS, Mich. — 18 stingrays and three bamboo sharks at John Ball Zoo have died after a circuit malfunction Thursday night.

Zoo officials made the announcement Friday afternoon.

According to officials a heavy rainstorm Thursday evening caused one of the two pumps for the lagoon to shut down. The backup alarm system also malfunctioned.

“It is with profound sadness we announce the loss of 18 stingrays and three sharks,” said John Ball Zoo CEO Peter D’Arienzo in a press statement. “This is a heart-wrenching incident, and we are mourning the loss of these special animals that brought so much joy and amazement to so many people.”

Officials say that at about 7:30 am Friday, staff found the deceased deceased cownose stingrays and bamboo sharks. They say they were able to determine immediately that the lagoon oxygen levels were too low.

Officials say that the storm had caused some flooding at the zoo overnight.

“We are currently performing a thorough investigation to confirm the cause of this tragic incident as well as a comprehensive system review of all the Zoo's aquatic life support systems,” said John Ball Zoo Chief Administrative Officer Andy McIntyre in a press release. “The John Ball Zoo is committed to providing the highest quality care for all of our 1,400 animals, which is why this incident is so devastating for the entire John Ball Zoo community.”

The stingray exhibit opened in 2007. Officials say they plan to re-open a new stingray exhibit in the future.

What caused the oxygen pump to fail is still under investigation, but zoo staff think it had to do with a GFI circuit tripping from Thursday night's flooding. That took a turn for the worse when the emergency alarm never registered the problem.

"The waterfall is what provides the oxygen and the GFI circuit tripped" said D’Arienzo. "When we came in this morning, we reset the GFI circuit and the pump started right back up."

Water samples were sent to two independent labs for testing and they hope to have a better idea of what happened in the next few days.

"We know the alarm failed, but we don't know why it failed" said D'Arienzo. "We know it is on a separate circuit and we know it gets its power from somewhere else, but for whatever reason the sensor didn't operate."

After losing 21 of their family members, representatives from John Ball Zoo says they'll do whatever it takes to make sure something like this never happens again.

"Right now we're focused on our grief" said D’Arienzo. "This is really tough, but we'll learn a lot more about it. Right now it's about those 21 members of our family."

PETA Foundation Associate Director of Captive Animal Law Enforcement Rachel Matthews released the following statement in response to the deaths at John Ball Zoo:

There are few exhibits deadlier than a touch tank, where sensitive aquatic animals are unable to escape a constant onslaught of groping hands that dirty and pollute the water with bacteria and where a single malfunction or mistake could suffocate and poison dozens of animals in one go. We saw it last night at the John Ball Zoo, and we saw it last year when an oxygen malfunction killed 54 cownose rays at the Brookfield Zoo. PETA is calling on the John Ball Zoo to take the only reasonable action here and close down the deadly touch tanks for good.