Day Trip From Calstock

I used to holiday in Calstock with my parents, staying with my grandparents who lived in the village.  I used to regularly take their golden Cocker spaniel, Vicky, for a walk up to the railway station. This was around the early 1950s to about 1956.
I remember being taken, with my parents and by a family friend, to a place which I think would have been perhaps up to an hour's car ride away - probably much less. I believe it was still on the Cornish side of the Tamar but we may have crossed to Devon. At this place I was able to swim. My recollection is that is was a sort of rectangular, stone construction pool, possibly spring fed as it was very cold! It wasn't a 'public' pool and wasn't all that large but I am unable to suggest how big it was. ( I believe it was fresh water.) I've read Roger Deakin's book, 'Waterlog', but can't find anything there!
Does anyone have a clue where this pool is (or was) situated? If not, perhaps the readers of a newspaper local to Calstock may be able to help?