The Environment Agency has urged children and young adults not to play in the Thames during hot weather this summer.

It follows a number of deaths in recent days.

Cold water shock can catch swimmers off-guard and strong currents are another hazard. It might also be impossible to see what obstacles lurk under the surface.

Russell Robson, waterways operations team leader, said: "The summer is always a busy time on our rivers, and we expect the River Thames to be a focal point for a lot of people’s leisure time, whether out in a boat, taking a dip, or just hanging out by the riverside.

"But we are urging parents and guardians to supervise younger children closely in and around water.

"Teenagers and young adults should be warned of the dangers and to remember some basic safety points when out having fun.

"One of the main risks is cold-water shock, which can have a dramatic effect on your body, such as causing you to breathe in water, make your muscles weaken, and can even cause your heart to go into abnormal rhythms, ultimately resulting in death.

"You also have no idea what’s beneath the surface of the water: there could be unseen currents and reeds, which could pull you under.

"In an ideal world, no one would get on or in the river alone, so there would be someone around to help if they did get into any difficulties.

"And anyone out in any kind of boat should wear a lifejacket, just in case.

"As for swimming in the Thames, we’d really rather people didn’t do it unless it’s part of an organised and supervised event.

"Swimming should be confined to swimming pools and lidos."