A pool at a disused Derbyshire quarry, known locally as the Blue Lagoon, has been dyed black in a bid to deter people from swimming in it.Despite the water at the quarry at Harpur Hill, near Buxton, having a pH level of 11.3 dozens of people still swim there.Bleach has a pH level of 12.3 and signs warn swimmers the water could cause skin complaints. Swimmers are also warned the water contains rubbish and dead animals. Read