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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Slowly brightening up later in the day, with some warm sunny spells possible by evening.
Any mist and low cloud will clear during the morning, leaving bright or sunny spells.
Beginning grey and murky again with extensive low cloud and some patchy rain.