Derbyshire's Blue Lagoon dyed black to deter people taking a dip in water that is nearly as toxic as bleach
But despite its appearance, the water held a dangerous secret - it is almost as toxic as bleach.
Now, in a bid to prevent people from bathing in the disused quarry at Harpur Hill, near Buxton, Derbyshire, the council has taken the incredible step of dying it black.
Dangerous: This disused quarry in Derbyshire - known as the Blue Lagoon - has been dyed black to prevent people from swimming in it
Damaging: Parents and children have swam in the waters of the Blue Lagoon for more than a decade. But the water is almost as toxic as bleach
Tropical: This picture shows how the Blue Lagoon looked before it was turned black
The water, which has a pH level of 11.3, is so dangerous it could cause fungal infection such as thrush, skin complaints and severe stomach problems.
Signs also warn swimmers that the water contains car wrecks, dead animals, excrement and rubbish.
However, when the weather warms up, swimmers largely ignore the warnings - prompting the drastic action to transform its colour.
Local business owner Rachel Thomas said she thought changing the colour of the quarry water has already made a difference.
Grim: The water also contains car wrecks, dead animals, excrement and rubbish
Mess: Rubbish bottles are pictured surrounding the waters of The Blue Lagoon
Hazardous: This warning sign was placed near the Blue Lagoon, but some swimmers still decided to take to the dangerous water
Ms Thomas said: 'It’s not pretty any more. They don’t think they’re on holiday in the Bahamas any more, they know they’re in Harpur Hill.
'It was absolutely beautiful to look at but was horrendously dangerous.'
The incredible blue colouring of the water is caused by the surrounding limestone rocks which leach calcite crystals into the water, turning it turquoise.
Worrying: Many signs warn people against entering the water. But despite this swimmers often ignore the advice during warmer weather
Unpleasant: This sign also details some of the nasty health problems which people can pick-up from swimming in the water
The alkalinity comes from calcium oxide, a white powder which would have originally been left around the site as a by-product of the quarrying process.
Councils have no powers to prevent trespass because the land is privately owned and the water can’t be drained into the water supply because it is so toxic.
A High Peak Borough Council spokeswoman said the pool contained vehicle parts, 'all sorts of rubbish' and warned that the water temperature was 'extremely cold'.
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