This is an original vintage Swimming Pool Rules Poster that I'm pretty sure hails from the 1980s. It's the update to the 'Will Patrons Kindly Refrain From...' version and has the super-period 'Beano' comic-type look.
This was issued by the Institute of Baths and Recreation Management. It's framed, with the frame coming in at 62cm x 78cm, the poster itself measuring around 45cm x 60cm. I haven't removed this from the frame, but am pretty sure it's laminated.
Personally, I can remember these from those school trips to the pool. A proper slice of 80s nostalgia... you can almost smell the chlorine.