Officers are investigating a racially aggravated hate crime that happened at about 3.30pm on 25 June, in the area of the Memorial Gardens.
A teenager is alleged to have made a racist comment to a lone female, causing her to feel threatened and upset.
The suspect is described as a 13-year-old boy. He was seen swimming in the river with other children around the time the incident occurred. He was wearing bright orange swimming shorts, no top and had mousy blonde hair.