A former urban explorer says the most unpleasant part of exploring New York City’s sewer system was the cockroaches, not the rats, smells or ever-present dangers.

There’s no threat to the public and officers have scoured the sewer system to make sure “nothing nefarious had been left behind,” a law enforcement source said.

Since May 5, at least three of the unexplained sewer incidents have been recorded in Brooklyn and Queens.