PSNI Foyle say on its Facebook page it was the second incident of the evening on the Foyle Bridge which had to be closed for a period.
During the first incident, police say volunteers from Foyle Search and Rescue successfully talked a person round to the right side of the bridge before they were secured by the PSNI.
Once the incident ended successfully, police reopened the Foyle Bridge to traffic only for a second person attempt to enter the water.
An officer wrote on PSNI Facebook: “Unbelievably as I was writing this another unrelated person attempted to climb over the railings and again some passing local heroes have intervened and the person is now safe.
“I just wrote the post about our brilliant city and then this happened.
“But again it has shown the very best of our city: people going out of their way to help others.”