The force has appealed for public assistance to trace a perpetrator who flashed near the lake in Parsloes Park at around 8am on July 27.
An e-fit image has been released of the man, who is said to be Asian and in his mid thirties.
A police appeal on Monday added that he is around 5ft 8 and was wearing grey jogging bottoms, a black jacket, and a black baseball cap.
Any witnesses or anyone with any information is asked to call police on 101 or contact via Twitter @MetCC, referencing crime number 7272/30JUL22. Alternatively, contact Crimestoppers on 0800 555 111.