The Blue Lagoon near Buxton, a flooded quarry - has inviting turquoise waters, but it is so polluted it's almost as toxic as bleach.
There are warning signs saying it can cause skin and eye irritations and stomach problems, but families and young swimmers are ignoring them.
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Mainly dry and rather cloudy this evening and overnight. Some clear spells may develop at times.
Showery rain spreading into the area overnight.
Good news for the weekend with sunny spells and warmer temperatures on the way. But, don't put your umbrellas away, yet.