Coastguards have renewed their warning to young people about risking their lives by "tombstoning" - diving off rocks and cliff faces.
Coastguards say 'tombstoners' must be warned of the dangers
It comes after police and coastguards were called to caution about 40 youths who were jumping off rocks near Babbacombe in Devon on Friday night.
A man died after tombstoning at Ansteys Cove in Torquay last month.
In Cornwall, a security firm has been employed to patrol Penzance harbour and the town's Jubilee Pool.
Brixham Coastguard said good weather has encouraged more young people to participate in tombstoning.
Spokesman Dave Scullian said: "Jumping off rocks or high locations into the sea is a dangerous activity and it must be discouraged.
"One slip or a jump in the wrong place could have dire consequences or end in tragedy."
Coastguards said they did not want to stop people enjoying the summer and having fun, but they must realise the serious dangers.