North Yorkshire Police is appealing for information about the assault close to Oakdale Place, near to The David Lloyd Leisure centre, at 11.15pm on February 8.
A woman in her fifties was grabbed from behind and aggressively pushed towards the hand rail of the footbridge, police said.
The suspect is described as a man, around six feet tal , wearing a dark hooded top and with “pointed facial features”.
"The victim shouted out and the suspect made off towards the Jenny Fields area. Fortunately the victim was not injured but obviously very distressed by the ordeal," a spokesman said.
Anyone with information can call 101 or email [email protected]
Quote the North Yorkshire Police reference number 12190024207.