The National Zoo says a chlorine-related incident on its grounds made a boom this morning—not “an explosion” as some local news outlets reported.

“There was an incident on the American Trail in which there was a loud boom but no fire and no smoke,” a zoo spokesperson, writes in an email to City Desk. “D.C. Fire Department is on scene investigating. No visitors, staff, or animals have been injured. American Trail is currently closed while the investigation is ongoing. Once we have a report back from them, we will send an update.”

A second zoo spokesperson said the incident occurred “near the otters and beavers area” along the American Trail, which is at the lower end of the zoo:

Update 1:20 p.m.: Zoo spokesperson Jennifer Zoon says the incident occurred around 11 a.m., when a contractor was doing routine maintenance work along the American Trail.

“He was in the mechanical room when he smelled chlorine, which the Zoo uses for water filtration in the life support system,” Zoon writes in an email. “Upon smelling the chlorine, he exited the building and the boom occurred shortly thereafter. In an abundance of caution, the D.C. Fire Department hazmat team is on scene to inspect the area. American Trail remains closed at this time.”

Update 2:50 p.m.: The zoo says fire officials have permitted zoo personnel to check on the animals near the trail. They seem OK:

Photo by Darrow Montgomery; map via Smithsonian National Zoo