Police and fire chiefs in South Yorkshire have issued a warning over open water swimming in warm weather.
Inspector Richard Batty, from South Yorkshire Police, said people should use swimming pools rather than taking a dip in reservoirs, lakes, canals and rivers.
He added: “We don’t want to stop people from enjoying any warmer weather this summer, but lakes, rivers and flooded quarries hide a multitude of dangers beneath the surface.
“Although the water might seem inviting, freezing temperatures, hidden currents and debris underneath the water can all pose grave dangers.
“The water can often be a lot colder than expected and swimming in freezing temperatures, even if the weather is warm, can affect your ability to swim and can soon mean you find yourself in some difficulty.
“With murky waters, it’s also unclear as to how deep a body of water can be. People can throw all sorts in rivers and reservoirs, from old bedding to car engines and this can cause severe injury, particularly if you’re jumping in from a height.
"Weeds can also grow underneath the surface, which can prove to be very dangerous."
Steve Helps, Head of Prevention and Protection at South Yorkshire Fire and Rescue, 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.
Members of the public are urged to call 101 if they spot people swimming in open water.