This is the alligator snapping turtle ...
A small example which was found on Monday 11th February 2024 by a dog walker in a Cumbrian lake has been nicknamed Fluffy. [Urswick Tarn, near Ulverston] The exotic creature is native to swamps and rivers in Florida USA, and is classed as an invasive species.

Fluffy’ was transferred to Kent’s National Centre for Reptile Welfare after being treated initially at Wildside Vets, Barrow. Director Chris Newman said: “Fluffy is doing fine now. He suffers from a condition called metabolic bone disorder which has left him with a soft shell. We are still treating him for that.

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en.wikipedia.org/wiki/Alligator_snapping_turtle