The Living Collections team at the National Mississippi River Museum & Aquarium in Dubuque, Iowa, has announced the Delta in the National River Center is closed. Stingray feedings and touch tank capabilities are on hold until further notice while staff and the veterinary care team investigate the deaths of eight stingrays on Thursday, according to the museum’s website.

Phoenix Zoo employees Linda Hardwick, top, and Kelsey Ray pet stingrays Thursday, April 9, 2020, in Phoenix. There’s a lot less foot traffic at the zoo since it closed to the public last month due the new coronavirus outbreak, and its animals are feeling the impact. Linda Hardwick, the zoo’s communication director said the zoo’s nearly 30 stingrays are also used to being frequently touched and handled, adding that staffers are taking time to give them “extra TLC.” (AP Photo/Matt York)

Upon arrival on Thursday morning, staff noticed animals in distress and immediately began steps to determine a cause. The exhibit appeared to have experienced a “supersaturation event,” following a malfunction in the life support system, causing gas embolisms, or gas bubble disease, in the animals. The exhibit’s monitoring system showed a spike in oxygen levels late Wednesday night, but did not send an alarm notification to staff as expected. The cause of the malfunction and lack of alarm notification is still under investigation, according to the website..

Five Cownose Rays, two Yellow Stingrays, and one Atlantic Stingray were lost. One Cownose Ray remains in stable condition, according to the website.

While preliminary reports suggest a supersaturation event, the cause of death will not be confirmed until necropsy results, water quality testing and toxicology reports are complete. Results could take up to several weeks.

“Our staff is heartbroken over this loss and are taking steps to ensure this does not happen in the future,” said Andy Allison, vice president of Living Collections and Education. “We are reevaluating our life support and monitoring systems for all exhibits including new systems being constructed within the Rivers to the Sea exhibit space. This is a difficult time for everyone at the River Museum and we ask for visitors’ patience and understanding as we provide care for our remaining stingray and move forward.”

The life support system maintains water quality and conditions in the exhibit, while the monitoring system ensures alarms and notifications are sent should exhibit conditions shift outside set parameters. The system is checked at least twice daily by trained aquarists on staff and the River Museum’s maintenance team. Initial indications point to this being a chance incident and steps are being taken to review the system.

The Delta is expected to reopen Friday, but touching and stingray feedings will be discontinued until further notice. The River Museum remains open during regular hours and visitors are asked to check the website for any updates related to the Delta exhibit.