A group of youths backflipped off Tower Bridge into the River Thames in a move that drew criticism online as the UK sweltered in the summer heat.
Footage of the “extremely dangerous” stunt posted on social media showed three young men spinning from the bridge in unison before a fourth followed.
The deck of the central London bridge stands around 30ft above the water level, though can be much higher at low tide.
A clip of the jumpers was posted to Instagram on an account named Adam Szaniawski, which links to a YouTube page under the same name featuring videos of urban exploring, a hobby which sees people making their way around remote or abandoned buildings.
Commenters on social media lined up to condemn the group for the stunt, with many noting the Thames is famously dirty.
When entertainer David Walliams swam down the river in 2011 he received several inoculations to ward off illnesses from the dirty water.
Adam Szaniawski was apparently aware the stunt was risky. He was quoted in The Sun as saying: “We were all buzzing off each other’s hyped-up energy that it almost felt natural.
“The current was strong and it was a difficult swim to try and get out. We thought about the dangers and I’m not encouraging people to do this.
“It took a lot of mental preparation and training beforehand. All of us had flipped off similar heights before.”
The Port of London Authority passed a bylaw in 2012 forbidding swimming in the Thames between the river mouth and Putney Bridge, a crossing west of central London known for being the starting line of the annual Oxford v Cambridge boat race.
The RNLI previously said jumping from Tower Bridge was “extremely dangerous” and advised against it.
A teenager who jumped from the bridge in 2015 said he regretted it after having to be rescued by lifeboats.
Britain is in the throes of a heatwave this week and authorities have warned the high temperatures could prove dangerous.