A man and women are believed to have been involved in an indecent act in Crick Road, Yelvertoft, on Tuesday afternoon.
The incident took place sometime between 4.10 and 4.30pm.
The man is described as white, around 5ft8” tall, in his late 40s, of medium build, with short balding, grey hair and was wearing a dark blue polo shirt and light blue jeans.
The woman was white, around 5ft9” tall, in her late 50s, of slim build, with shoulder length dark, greying hair and was wearing a knee length blue cardigan with a white top underneath.
Witnesses to this incident, or anyone with information, should call Northamptonshire Police on 101 - alternatively, information can be given anonymously to Crimestoppers on 0800 555 111.