This is something that gets commented on again and again, even many years after my original post on one of the locations. I think the main reason for all the confusion is there are at least three sites, all in disused whinstone quarries, all look similar.
The name ‘Blue Lagoon’ never appears on maps either so your ‘Blue Lagoon’ might not be someone elses ‘Blue Lagoon’
I believe the location most people who visited in the 1970’s would have known as the Blue Lagoon was around Langbaugh Quarry and Nunthorpe Quarry, between Great Ayton and Nunthorpe, now the location of the Whinstone View Bistro.
The 1970s OS map shows three pools here, which also ties in with peoples recollections of being able to dive under the water and emerge in other areas.
This location no longer exists, it was filled in, as you can see from aerial views today.
In more recent times people have started to call the Donkey Pond the ‘Blue Lagoon’, this is about 0.5 mile E of the Gribdale Gate car park, also an old whinstone quarry.
The third location is Lonsdale Quarry which is on private property about 0.5 miles NE of Kildale. This location was used by Jack Hatfield to practice swimming for the 1912 Olympics.
Over the years i’ve picked up a couple of photos, its hard to say which location is which and i’m afraid I don’t recall where I got them from so if they are yours let me know so I can credit you.
Ray Simpson between Great Ayton and Nunthorpe 1958 / 59