A pool at a disused quarry in Derbyshire known as the Blue Lagoon has been dyed black in a bid to deter people from swimming in it.
Boasting a turquoise colour more normally associated with a Caribbean beach, swimmers at the quarry in Harpur Hill, near Buxton, had previously ignored signs warning of its dangerous pH level of 11.3 - and taken a dip in there.
Bleach has a pH level of 12.3, and swimmers were warned that the water - which gets its colour from caustic chemicals in the quarry stone - could cause skin complaints or stomach problems, as well as being filled with rubbish,
A High Peak Borough Council spokeswoman told the Daily Telegraph: "It has similar pH levels to bleach and is extremely cold. There are also a number of hazards, there was a car abandoned in there and all sorts of rubbish, but it still looked a lovely turquoise colour.
She added that there were already anecdotal evidence the move is working as residents said that over the weekend people were coming up as they normally do to swim "and then very quickly turning around again when they saw the water".
Local business owner Rachel Thomas said she thought changing the colour of the quarry water had made a difference.