A man was seen performing a sexual act on himself at a York nature reserve.
North Yorkshire Police said it happened in Clifton Backies between 2pm and 3pm on Tuesday, July 16.
The man was then seen running further into Clifton Backies near the entrance by Woodland Chase, a force spokesperson added.
He is described as white, skinny build and around 5ft 9in and was wearing a black hooded top, white tracksuit trousers, black trainers and a black backpack.
Police today (Thursday, August 1) urged anyone who recalls seeing a man matching the description or who has information about the incident to get in touch.
Those who can help should email adam.lukins2@northyorkshire.police.uk or call 101, select option two and ask for Adam Lukins.
Crimestoppers can be contacted anonymously on 0800 555 111 or via its website.
Quote police reference number 12240126513 when passing on information.
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