The Environment Agency has issued a plea for people not to take 'unnecessary risks' by jumping off or swimming near its river structures.
It asked people not to be tempted by the heat and to pay attention to warning signs, saying swimming too close can be dangerous and "could lead to serious injury or death." It is also an offence.
The EA owns and maintains areas such as locks and sluices across East Anglia’s river network and on the coast.
Paul Separovic, waterways team leader, said: "We work to advise on the safety risks connected with our river structures in partnership with local councils and landowners.
"Throughout the summer period, we see people put themselves at risk by ignoring advice and swimming in dangerous places, which can have serious, even tragic, consequences."
The structures display warning signs that highlight the impact of strong currents, underwater structures and sudden changes in depths, which the EA says can all pose a serious risk to even the most experienced swimmers.
The EA added: "Those who ignore the warnings are not only potentially putting their lives at risk but also committing an offence that could lead to a day in court and a fine of up to £1,000.
"Jumping or diving off the assets - which include weirs, sluices, locks and pumping stations - is strictly prohibited and could cause serious injury."
Last June, police broke up a group of 70 young people who were jumping into the water off mooring and swimming in the Wiggenhall St Mary Magdalen and Watlington area.
And in 2019, children and adults were seen jumping off a bridge over the Great Ouse Relief Channel in Watlington.
The EA had offered tips for staying safe around rivers, which include not jumping or diving in as the depth may vary and there can be unseen hazards, not to go near weirs, locks, pipes, and sluices, being aware of how cold inland waters can be, and keeping an eye out for boat traffic.
For more information on the EA's tips and on knowing if an offence has been committed visit here.
The EDP has launched the 'Play it Safe' campaign, which urges people to enjoy the county's waterways safely.
It is encouraging businesses to help spread the water safety message by displaying the Play It Safe poster in their windows.
David Powles, EDP editor, said: "Norfolk and Suffolk are blessed with some wonderful places to enjoy water, with miles and miles of stunning coastline and the beautiful Broads.
"However, in recent years there have been several signs that perhaps people are not fully aware of the dangers which can lay beneath and are not fully preparing themselves before going into the water.
"In 2020 we sadly saw several tragedies both on the coast and inland and already this summer there has been one tragic death of a young man.
"We want to spread more awareness to those looking to enjoy our waters and hope this campaign will do just that, plus encouraging shopkeepers and businesses in popular areas to display our specially designed posters."
The posters can be ordered for free, with only a small charge for postage and packaging, from www.norfolkstore.co.uk/store.
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