NEW YORK — Law enforcement agencies are investigating three incidents of unauthorized entry into New York City's sewer system. Surveillance footage recently recorded small groups entering and exiting sewer tunnels in Brooklyn and Queens.

Police have determined these recent sewer entries do not present a threat to the public. Recorded footage indicates some individuals remained underground for approximately three hours during their excursions.

Steve Duncan, a former urban explorer, suspects the individuals recorded on video were urban explorers navigating 19th-century sewer mains. Duncan documented tunnel systems beneath New York City during the early 2000s.

New York City maintains approximately 7,400 miles of underground sewer pipes. Some sewer mains in the city measure over 6 feet in diameter and feature historical brickwork and arched ceilings. Several underground sewer channels were constructed over natural waterways prior to industrialization.

Sewer exploration involves navigating humid conditions, slippery surfaces, and flowing water that can exceed one foot in depth. Duncan recalled that encountering cockroaches was the most unpleasant aspect of exploring New York City's sewer system. "They're all over the place, crawling on walls, dropping down on you," he said. "They were the worst."

Heavy rainfall preceding the recorded events likely reduced the volume of water and waste flowing through the sewer system. Conducting sewer explorations during early morning hours typically results in lower waste flow compared to daytime hours. Individuals recorded in the sewers were observed wearing waterproof hip waders and carrying headlamps and tools.

Unauthorized entry into New York City sewer infrastructure is prohibited by law. Magued Iskander, an engineering professor at New York University, noted the potential uses of sewer systems for criminal activity. "Sewers can serve as entry or exit points to buildings, and we have all seen movies in which criminals escape jail through a sewer," Iskander said. "There must be a reason beyond mere thrill to enter a dirty place like a sewer."

David Sarni, a retired New York Police Department detective and an instructor at John Jay College of Criminal Justice, said the footage shows potential security vulnerabilities in municipal utilities. "Is this something that could be exploited by people who look to do harm?" Sarni asked. "You have to really take nothing for granted and always think, unfortunately, on that negative side."

Duncan said that urban explorers are typically not looking for valuables. "These are terrifying places that take a lot of planning and dedication to explore safety," he said. "You don't do all of these things for the tiny chance of finding a diamond earring."