Harper Hill Quarry (Blue Lagoon), Buxton

Limestone quarrying in the Harpur Hill area dates back to at least the 1600s, with small-scale lime burning taking place around Grinlow near Poole's Cavern. By 1835, large-scale lime production had begun beside the quarry, using larger shaft kilns and later a multi-chambered Hoffmann kiln. The operation was managed by Buxton Lime Firms Ltd, which eventually became part of Imperial Chemical Industries.

In 1938, the Royal Air Force (RAF) acquired the site to establish RAF Harpur Hill, a chemical weapons storage depot. By 1940, it had become the UK’s largest facility of its kind, covering approximately 500 acres and storing various chemical munitions, including mustard gas and phosgene. After the war, the RAF used the site to dispose of captured German chemical weapons by burning them with bleach on the surrounding hills—a method that was only partially effective, as escaping mustard gas vapour damaged nearby vegetation. The depot was decommissioned in 1960.

Following the quarry’s closure, a flooded section formed a lake known as the "Blue Lagoon." Its striking turquoise-blue color is caused by light scattering off fine calcium carbonate particles. The water is highly alkaline, with a pH of 11.3, due to leaching from lime-burning residues. Despite health warnings, the lake became a popular tourist attraction. In response, local authorities dyed the water black in 2013, 2016, and 2020 to discourage visitors, though the blue hue often reappeared.

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