Young people who jump from high bridges and harbour walls into water unsupervised are dicing with death, council bosses have warned.
The Local Government Association (LGA), which represents dozens of councils and fire and rescue authorities across the country, has reported a summer holiday surge in the activity known as tombstoning.
Figures suggest tombstoning has led to two deaths a year over the past decade.
The LGA is calling on the Government to raise awareness of the dangers of jumping into water and of cold water shock by extending a campaign run by the Maritime and Coastguard Agency to schools across the country.
At the moment the campaign is targeted at men aged between 18 and 29, but the LGA believes it should be tailored and rolled out to schools to make younger people aware of the risks.
Simon Blackburn, chairman of the LGA's safer and stronger communities board, said: "Tombstoning is extremely dangerous and grim statistics show that anyone doing it could kill themselves or end up with life-changing or serious injuries.
"Jumping into water may appear enticing during warm weather, but you should never jump off any structure directly into the sea or a river as you can never be sure how deep the water is below.
"Shallow water, unseen objects under the water, hitting something on the way down or simply landing badly can lead to people being killed or paralysed.
"The message is clear - if you don't know that the depth of the water is safe or you cannot see what is below the surface, don't jump."
The coastguard dealt with more than 200 incidents of tombstoning between 2005 and 2015.
Those incidents resulted in 83 injuries and 20 deaths.
Councils are also warning about the danger of cold water shock and of swimming in the sea and open water.
The warning comes after five people died during a beach day trip to Camber Sands in East Sussex.
Mr Blackburn urged the Government to act quickly to increase awareness.
He said: "Young people across the country, not just those living near the sea, need to be aware of the dangers as they also relate to inland rivers and canals.
"We are calling on the Government to extend a campaign by the Maritime and Coastguard Agency on the dangers of jumping into water and cold water shock to schools nationwide as the dangers exist for everyone, particularly vulnerable teenagers playing games of dare."