Thames Valley Police is appealing for information following an incident of indecent exposure in Milton Keynes.
At around 2.35pm on Saturday (November 19), the victim, a woman in her late 30s, was walking with a teenage girl and a child along the redways throughout Downhead Park and the surrounding areas.
They were walking near the canal when a man on his bicycle cycled past them.
The same man was then seen a short while afterwards underneath a bridge, in front of the victims, standing astride his bike but not moving.
As the victims reached and crossed a different bridge, they saw the man behind them, cycling very slowly.
The victims continued their walk.
A little while later, the victim saw the man cycle past her very quickly.
She continued her route and as she reached Colesbourne Avenue the man stepped out from behind a tree and was masturbating while staring at them.
The victim shouted at him and the offender pulled up his trousers and cycled away, into Downhead Park.
The offender is white, about 5ft 7ins or 5ft 8ins, of medium build and bald with no facial hair.
He was wearing a black waterproof-style jacket and blue jeans, he was riding a blue mountain bike which had a seat that was thick and chunky.
PC Rebecca Wade, said: “Offences like this will not be tolerated in Milton Keynes. I would urge anyone with any information to come forward.
“If you do not want to speak directly to the police you can contact the independent charity Crimestoppers anonymously on 0800 555 111.”