After a lot of pestering I eventually went lake swimming with my friend Lesley and (pictured) Glenn.
Here is the before shot at Bewl Water. We were reliably told that the water temperature was 19C, I can categorically tell you it was closer to -19C. Once over the initial shock and actually swimming, it was quite refreshing though.
The course was only 400m and I think I could have done it again. Maybe next time.