'Someone is going to die': warning over tombstoning
Teenagers photographed jumping into the water from bridges at Salford Quays in Greater Manchester have been warned that they were "risking their lives".
A former lifeguard saw the group plunging into a basin of the Manchester Ship canal.
He said some of the children seemed as young as ten.
The temperature contrast can trigger "cold shock" - and it can even cause a heart attack.
Anyone caught jumping into the water can be prosecuted after Salford council introduced a Public Spaces Protection Order across the Quays area earlier this year in a bid to clampdown on the dangerous behaviour.
Daredevils caught jumping into the water could face a fine of up to £1,000.
Town hall chiefs said they have even offered open water swimming sessions at Salford Watersports Centre, but still the issue remains.