The 18-year-old victim was cycling along Clifton Bridge in the direction of Acomb, at about 1.05am on Saturday 23 July 2011, when four unknown men stopped him in the road.
They forcibly took him to the bridge railings and searched his pockets, removing his wallet, mobile phone and passport. They then pushed the victim back against the railings and he fell about 8 metres into the River Ouse below.
The man initially went under the water but was able to swim to safety without any apparent injury. He found his stolen possessions on the pavement over the bridge. A small amount of cash had been taken from the wallet.
The victim was unable to provide any descriptions of the suspects. Officers are scanning CCTV footage in the area to help identify those involved.
PC Pauline Law, of the York Safer Neighbourhood Team, said: “This was a dreadful incident which could easily have ended in tragedy. It is simply down to good fortune that the victim was able to swim to the shore. If he had hit his head or got into difficulties in the water, then the offenders would have a death on their consciences as well as the robbery itself.
She added “We are following a number of lines of enquiry including a public appeal for witnesses or anyone with information about those involved that could help the investigation.
“Even the smallest piece of information could be very helpful, so please do not hesitate to contact North Yorkshire Police.”
If anyone can help the investigation, please telephone North Yorkshire Police on 0845 60 60 24 7, quoting the reference number 12110122153. Pass information for the attention of DC 1174 Michael Johnston at York CID.
Alternatively, contact Crimestoppers anonymously on 0800 555 111.