Fire chiefs in South Yorkshire have issued a warning about open water swimming ahead of the warm spell expected over the Bank Holiday weekend.
South Yorkshire Fire and Rescue said it 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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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.
"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."
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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."