The man was seen touching himself inappropriately in woodland close to the Stag Lodge car park – near the A49/A6 junction in Bamber Bridge – at around 6.45pm last night (Monday, August 1).
It was reported to police and visitors are now being urged to remain vigilant when walking through the park.
No arrests have been made at this stage but Lancashire Police is investigating.
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The force is asking anyone with information to get in touch on 101, quoting log 1192 of August 1.
Cuerden Valley Park Trust – which maintains and manages the site – alluded to the incident in a social media post today.
The Trust said: “The trust has been made aware that an incident occurred in the woods close to its car park at Stag Lodge, adjacent to the A49/A6 junction at Bamber Bridge, at approximately 6.30pm on Monday, August 1.
“We are unable to provide any further details at this time as the incident is being investigated by the police.
“Members of the public were not at risk, however we ask if you noticed anything concerning around the time or anyone acting suspiciously, please report it on 101 quoting the above log number.”
What do police say?
A police spokesperson added: “It looks like a report of a man seen touching himself inappropriately.
"We were called at around 6.45pm. No arrests as yet but anyone with information should call 101, quoting log 1192 of August 1.”