They have released photos of a dark-coloured, four-door car that was seen in the area of King and Frederick streets on the night of Aug. 29.
Police said they received a report of a sexual assault after a man picked up a woman in the area and drove her a park where the incident took place.
The suspect is described as a 20- to 40-year-old white man with a thin build.
Anyone with information is asked to call Waterloo Regional Police at 519-570-9777 ext. 8347 or Crime Stoppers at 1-800-222-8477.