People basking in the bank holiday sunshine who decide to take a dip in open waters are risking their lives, firefighters have warned.
South Yorkshire Fire and Rescue attends dozens of water related incidents each year - some of which involve rescuing people from open water - particularly during hot weather.
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Fire chiefs warned people who take a dip in waterways where swimming is prohibited are putting themselves in grave danger.
Area Manager Steve Helps, said: "We regularly receive 999 calls in the summer about people getting into difficulty in water, so it’s only a matter of time before someone’s safety is really put at risk unless people listen to our advice.
"It can be tempting to cool off in the summer months, but stick to a swimming pool.
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"Hundreds of people drown each year in the UK and places like rivers, lakes or flooded quarries are completely unsuitable for swimming as they hide a number of hidden dangers."
Over the last two decades a number of boys have died while out swimming in Manvers Lake in Wath-upon-Dearne.
In 1997, Darren Baggley from Wath-upon-Dearne, drowned when he suffered cramp as he swam with friends.
Adam Peterson, aged 18, from Goldthorpe, suffered the same fate in 2005 as he tried to swim out to an island with friends on a sunny day.
Philip Law, aged 15, of Rawmarsh, died of drowning in 2010.
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A fire service spokesman said: "Over 400 people die in the water every year in the UK.
"The water can be much deeper than you expect; rivers, lakes, canals and reservoirs are much colder than you think and open water can carry water borne diseases, like Weils disease.
"Cold water dramatically affects your ability to swim and there may be hidden currents, which can pull you under the water.
"You don’t know what lies beneath, like pieces of rubbish or reeds which can trap or injure you."