A man indecently exposed himself to two joggers at Pitsford Water, near Brixworth.
The man walked towards the two women at about 11.30am on Friday, March 25, on the Causeway.
He exposed himself before getting in a car and driving away.
The man is described as white and unshaven. He was wearing a navy hoodie, white trainers and navy tracksuit bottoms.
Witnesses, or anyone with information, are asked to contact Northamptonshire Police on 101.
Alternatively, they can call the independent charity Crimestoppers anonymously on 0800 555 111 or use the anonymous online form at www.crimestoppers-uk.org.