A series of baffling sightings of people entering the sewers in New York City has resulted in police launching an investigation. Surveillance footage has documented at least three incidents of people either entering or exiting the tunnels through manholes on streets in Brooklyn and Queens. Police suspect that the individuals were searching for valuables that had fallen into the sewage network, NBC News reported. It remains unclear if it is the same group of people involved in all of the incidents. The New York Police Department has reported no injuries or arrests related to the incidents. Authorities have urged people from entering the sewer system, as it is “both illegal and extremely dangerous,” said a spokesman for the New York City Department of Environmental Protection.