An 11-year-old boy has died after leaping 18ft (5.5 metres) from a bridge into a canal as part of a “tombstoning” game in Rotherham. Separately, police said they had found a body in the search for a woman who was feared to have drowned while playing in a river in Bedford with her children.

Police were called after the schoolboy disappeared into the canal in Rotherham, South Yorkshire, at about 7pm on Thursday. A search and rescue operation recovered the boy’s body at 11pm.

The incident will prompt fresh warnings about the danger of tombstoning – where thrill-seekers leap from cliffs or bridges into water – following a number of deaths across the UK in recent years.

Gary Willoughby, a watch manager at South Yorkshire fire and rescue service, told reporters at the scene that the boy had jumped 18ft from a bridge.

Willoughby said: “This 11-year-old boy was actually taking part in a pastime that boys of his age call tombstoning. Unfortunately it’s aptly named. It’s jumping from unknown heights into unknown depths of water.

“They tend to jump straight into the water. They don’t assess the water temperature, they don’t see if there are any dangers hidden under the water – shopping trolleys, cars, anything like that, any reeds they might get tangled in. They don’t even assess how deep the water is before they jump. “It’s a very dangerous pastime. Unfortunately this boy lost his life. I have heard of other people that end up in wheelchairs for the rest of their life. I’d like to send my condolences to his family at this time. It’s been going on for years and years. Even when I was a boy, people were doing this. My motto is: ‘no lifeguard means no swimming.’ Stay away from canals and rivers

Two hours before the boy disappeared police in Rotherham had urged people not to go swimming in open water.

In a post on Facebook, the Rotherham North local policing team said it had dealt with numerous reports of such incidents in the first few days of the school holidays. Emergency services were concerned that the start of holidays, combined with the unusually hot temperatures, could prompt young people to engage in the activity.

In Bedford, a body was found by police searching for a mother of three, thought to be in her 30s, who was last seen more than 14 hours previously when she was diving into a shallow part of the river Great Ouse.

Firefighters and divers had joined the search for the woman.

Joe Vacchio, who lives nearby, said there were screams of “I can’t swim” before police and a helicopter arrived. He said the woman lives around the corner from the river and had been diving into the water off small islands with her three children.

In a statement about the 11-year-old boy in Rotherham, a South Yorkshire fire andrescue service spokesman said: “We are all devastated by this tragic incident and our thoughts are with the family and friends of the boy who died.” 

The service said there had been 49 incidents involving rescuing people from open water since 2012. People died in three of those incidents.

South Yorkshire police said: “Police received a report at around 7pm that a boy had been seen entering the canal, off Stone Row Way, but had disappeared soon after.

“Specialist resources attended the scene, including South Yorkshire fire andrescue and the ambulance service. The body of the 11-year-old was found in the water at around 11pm. His family has been informed and are being supported by officers. The circumstances are under investigation.”

On Tuesday a 16-year-old boy drowned while playing with friends in a river in Greater Manchester on the hottest day of the year. Jack Pullen was in the river Etherow when he got into difficulty.

Officers said that while the river appeared shallow and calm there might have been strong undercurrents and hidden hazards beneath the surface. Detectives are investigating reports that the boy became trapped between a bridge and a log.