GRAND RAPIDS, MI - Eighteen stingrays and three sharks died overnight at John Ball Zoo, the zoo announced Friday, July 8. A mechanical malfunction that left the Stingray Lagoon pool low on oxygen is the likely cause of death, according to zoo officials.

A backup alarm that could have alerted zoo staff to the problem also failed to work, the zoo said.

"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 Andy McIntyre, the zoo's chief administrative officer, in a prepared statement.

It is with deep sadness that we announce the loss of our 18 cownose stingrays and three spotted bamboo sharks that lived... Posted by John Ball Zoo on Friday, July 8, 2016

Zoo staff found 18 cownose stingrays and three bamboo sharks dead in their pool Friday morning at the zoo, 1300 W. Fulton St. in Grand Rapids. A circuit malfunction caused one of two pumps for the pool to shut down, zoo officials said.

The stingray pool is one of the more interactive exhibits at the zoo, giving visitors a chance to touch the animals in the water. A new stingray exhibit is part of a new master plan for the zoo.

Matt Vande Bunte writes about government and other issues on MLive. Follow him on Twitter and Facebook.