RECKLESS youths who posted footage of themselves "tombstoning" in Trearddur Bay on YouTube are putting themselves in "extreme danger".
The video clip, uploaded on to the website on July 5, features a group of lads from the town jumping into the sea from a precipice in Trearddur Bay.
Hazards involved in the activity include low tide, submerged rocks or objects and strong currents, and RNLI's Holyhead spokesman Ray Steadman advised caution.
He said: "Obviously this is a very dangerous occupation, there have been many injuries and even deaths due to it.
"It's something you might do for years and get away with it but then you might go back at a low tide and get seriously hurt.
"Kids need to have fun, we all need to have fun, but you've got to be careful."
Holyhead town councillor Cliff Everett added: "Youths need to know the dangers and parents should be aware if their youngsters are doing this.
"There have been tragic incidents in the area so they have to be aware of the extreme danger in doing this."
Tombstoning involves jumping or diving from a height into water and has been labelled a high-risk activity, which is unregulated and is usually undertaken without supervision.
North Wales RNLI spokeswoman Danielle Rush said: "Check for hazards in the water, check the depth of the water, never jump while under the influence of alcohol, drugs or peer pressure and check for access, it may be impossible to get out of the water."