The dangers of open water are being highlighted after several incidents of people swimming outdoors.
Police say they have had reports of people going in the water at Denham Quarry and Birkacre.
And Beckie Ramsay, whose son Dylan died in 2011 after swimming at Hill Top Quarry in Whittle-le-Woods, says people have been in the water there.
It has led to them urging people not to go into the water to cool down on hot days.
PC Ian O’Brien, from Chorley police, said: “Because of the hot weather, they have been going into quarries swimming. We have had quite a few concerned people phoning up.
“It might be very hot outside, but the coldness of the water could kill them.”
Beckie, of Church Hill, Whittle-le-Woods, now campaigns to raise awareness of the dangers of outdoor swimming in memory of 13-year-old Dylan.
They include cold shock, water currents and debris in the water.
She said: “There have been a lot of deaths over the last couple of weeks. People need to be aware of the risks.”
She believes the water in quarries should be dyed black to make them less appealing to swimmers.
Beckie said: “I would love to see at least all the disused quarries across the country to be dyed black.
“I know this will not bring Dylan back to me, but it could prevent other families from feeling the pain that ours does.”