Former quarries often flood, forming swimming holes perfect for dangerous leaps off of cliffs, and horsing around with friends. Unfortunately they can also have some nasty residues left over from their industrial days.

In the case of the blue lagoon, calcium oxide, used as part of the quarrying process, has left the lagoon with a pH of 11.3, compared to ammonia’s pH of 11.5 and bleach’s pH of 12.6. If that is not enough, the site has been used as a dumping ground. Signs leading up to the lagoon read:

“Warning! Polluted water. Lagoon known to contain: Car Wrecks, Dead Animals, Excrement, Rubbish” and “Warning! Do not enter water, due to high pH levels. This can cause: Skin and eye irritations, Stomach Problems, Fungal infections such as thrush” and “Think! would you swim in ammonia or bleach?”

However the draw of the turquoise water, turned green as limestone rocks leach calcite crystals into the water, is simply too alluring. Families drive to the lagoon and children regularly go swimming in it with the simple warning not to dunk their heads or swallow any water.

Update: The area town folk are hoping to get it closed up. They recently tried to get it drained but were told the lagoon was too toxic and dangerous to the water supply to be drained.

Update: In June 2013, the council took the drastic measure of pouring black dye into the water to lessen its appeal. So far the plan seems to be working – according to locals, disappointed weekend road trippers have been turning back when they spot the newly inky lagoon.

Update: As of Summer 2015 the lagoon had turned back to its lovely blue hue.

Update: As of early 2018 the lagoon is now black and been told by police it will continue to be like this for the foreseeable future so swimming not advised as it could dye your skin.