There is a warning for families tonight after hundreds of people have been putting themselves at risk by swimming in toxic water in Derbyshire.
The blue lagoon near Buxton is actually a flooded quarry.
The water there looks similar to the clear blue seas you might expect to find in an exotic foreign location but that is because it contains limestone.
Environmental experts say the water causes skin and eye irritations as well as stomach problems, but families and young swimmers keep on coming. Our correspondent, Matt O'Donoghue, reports