A campaign is underway to stop people flocking to a beauty spot, dubbed the 'Blue Lagoon' in Buxton.
The unusually bright blue water makes it look like a Mediterranean paradise but experts say it's PH levels make it almost as toxic as bleach.
Residents say they're concerned because hundreds of people have been taking a dip to cool off in the warm weather but the water could cause stomach and skin problems.
The blue colour of the water is caused by the surrounding limestone rocks which turns it into what looks like a little bit of paradise when instead the site comes with a health warning.
Signs close to the shoreline warn the water could cause skin and stomach problems. Other warnings including ones stating the water is known to contain abandoned cars and human waste, but it has a pH level of 11.3 – compared with 12.6 for bleach.