A man needed hospital treatment for a head injury following an alleged assault in the changing rooms at Havre des Pas pool.
Police want to speak to anyone who was at the Lido at around 7am on Tuesday (18 March).
It's believed an object was used in the assault, although the force says it is not known what that was.
The suspect was arrested later the same day at police headquarters.
He was wearing hi-vis orange trousers and a blue jumper and was holding a yellow JD Bag.
"Anyone who may have seen this or who has any information is asked to contact police on 612612 or the independent charity Crimestoppers anonymously on 0800 555 111 or via their anonymous online form at Crimestoppers-uk.org"
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