The sewer people are at it again.

The NYPD is again investigating a report of people seen exiting a manhole, this time on the Upper East Side.

Police officers responding to a call around 4:30 a.m. were told by a witness that three people had climbed out of the sewer system in front of 535 Park Ave., according to the NYPD. The three unidentified individuals then got into two separate vehicles, driving away northbound on Park Avenue.

It’s the latest instance of people being spotted apparently moving through New York City’s underground infrastructure this year. In August, five people were spotted exiting a manhole near Penn Station. There were sightings of similar activity in Brooklyn in May, when two groups of seven and eight people were seen entering manholes in Gravesend and Williamsburg and emerging hours later.

A spokesperson for the city’s Department of Environmental Protection said the agency has inspected the sewer and confirmed that the infrastructure is safe. The DEP stressed that entering the sewer system is both illegal and extremely dangerous, as they contain numerous hazards, including noxious and potentially deadly gases, unstable surges, flooding risks and confined spaces.

Police said no arrests have been made in connection with the incident, and that an investigation is ongoing.