Waimea Bay beach was reopened Thursday morning after it closed Wednesday afternoon, when a diver discovered a mysterious, submerged metal object in waters near the offshore jump rock, the Honolulu Department of Parks and Recreation said in a press release.

The diver alerted City and County lifeguards about the object, and due to concerns it might be unexploded military ordnance, “access to Waimea Bay Beach Park was restricted out of an abundance of caution for public safety” while the object was examined, DPR said.

After inspection, the object was determined not to be ordnance, but possibly a compressed gas cylinder “such as a carbon dioxide canister,” the agency said.