Farrell Theis, 61, of Romeoville is charged with Child Pornography by a Sex Offender.
Theis is accused of taking pictures last month of young boys at a park district pool on West Jefferson Street in Joliet, police said.
A staff member at the Joliet Park District facility told officers Theis was an employee of a third-party company that serviced vending machines at the facility.
Detectives said Theis is a registered sex offender, and images of the high school swimmers were recovered from his cell phone.
Theis was arrested during a traffic stop this week.
No further information was immediately available.