Investigators from an FBI evidence-collection team are searching the Schuylkill River near the Falls Bridge.
FBI spokeswoman Carrie Adamowski said members of the bureau's Underwater Search and Evidence Response Team are searching the river this morning.
She said the investigators from the New York-based team were called to that site for a specific reason, but wouldn't give further details about what sparked the search or what the divers were looking for.
Divers from the unit are trained to use "sophisticated equipment" to "conduct traditional underwater searches to locate recover evidence and human remains," according to the FBI.
Adamowski said the searchers would be at the site as long as necessary, potentially a couple of days.