Rescuers in Devon and Cornwall are warning that it is only a matter of time before someone is killed while "tombstoning" along the coast.
Tombstoners may not be aware of tides where they are jumping
The craze of jumping off high ledges or cliffs into water is causing increasing problems for emergency services.
One teenager was injured after jumping off Plymouth Hoe on Tuesday night. There has also been an increase in the activity at Whitsand Bay in Cornwall.
Lifeguards and lifeboat crews also said people can suffer serious injuries.
There is nothing illegal about tombstoning, but it is a problem for the emergency services when things go wrong.
Last year a man in his 20s died after jumping off cliffs at Ansteys' Cove at Torquay.
Dave Milford, of the RNLI in Plymouth said: "Obviously we've all been children once and we've all done daft things.
"But when I see where they are jumping into off the Hoe, they obviously have no idea of the state of the tide.
"And with the treacherous rocks underneath, spinal injuries and neck injuries are going to be the first thing they come up against."
Whitsand Bay senior lifeguard Michael Bulley admitted that little could be done to stop the activity, but added he hoped educating people about the dangers might help prevent injuries.
He said: "People don't realise how quickly the tide drops back and how little water could be underneath them when they jump.
"We can advise people of the dangers, but we haven't really got any jurisdiction to keep people off the rocks.
"All we can do is speak to them and we let them know what could potentially happen if they do jump."