Groups of kids are swimming in a lagoon in Derbyshire which is almost as toxic as bleach.
Warning signs surround the flooded former quarry but children and families are ignoring them.
Kids are still swimming there because the water is really blue and looks clean - but this is due to the limestone hills surrounding it.
The water also contains abandoned cars, dead animals and human waste.
It's so toxic that swimmers can suffer from itchy skin and stomach problems.
Nearby residents are calling for action to stop people from visiting the site.
Hayely went along to find out more.