People are being urged to stick to swimming pools to cool off during the heatwave - after youngsters were spotted jumping into the River Don at a Doncaster beauty spot.
Police, fire and Yorkshire Water chiefs have all pressed home the message of not swimming in open water after a group of young children were spotted jumping into the River Don from a bridge near Sprotbrough.
A group of youngsters were spotted jumping into the water from a bridge near the Boat Inn and the passer-by said: "It’s generally the same place every year.
"Something needs to be done about it to stop it happening.
"It’s common for grown ups to do this in the summer months which is one thing and still very dangerous but when there are children doing it, it worries me as they really don’t understand the dangers.
"I wonder if these parents know where their children are and what they are doing and how dangerous it is?"
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.
And fire chiefs have warned people who take a dip in waterways where swimming is prohibited are putting themselves in grave danger.
A SYFR spokesman 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."
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.
And Philip Law, aged 15, of Rawmarsh, died of drowning in 2010.
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."
With water temperatures as low as 12ºC, depths of up to 50m in some reservoirs and undercurrents lurking beneath the surface, open water swimming has many dangers.
Alastair Harvey, Recreation Advisor at Yorkshire Water, said: “Reservoirs may look tempting to take a swim in but they can be killers.
"Cold water shock can lead to hyperventilation, increased blood pressure, breathing difficulties and heart attacks plus water temperatures remain just as cold in summer as in winter.
“We have 115 scenic and beautiful reservoirs that we want walkers, cyclists, runners, picnic-goers and others to enjoy this summer. We just don’t want anyone to swim in them and to obey our warning signs.”