Sept. 16 (UPI) — Organizers of the World Stone Skimming Championships in Scotland said a cheating scandal led to the disqualification of several competitors.

The World Stone Skimming Championships, an annual celebration of the sport also known as stone skipping, is held every September on the western Scotland island of Easdale.

The rules of the competition require the stones thrown by competitors to skim across the surface of the water to be naturally occurring slate from the island, but several competitors in this year’s event were found to be wielding rocks that appeared to have been shaped and smoothed by machine.

Some of the stones appeared to have artificial notches created to aid in throwing.

“I got calls from concerned competitors. They were worried people might think that’s how things are done here,” Kyle Mathews, the event’s “Toss Master,” told The Scottish Mail. “I contacted the individuals, who admitted their transgressions and I had to disqualify them. To give them their credit, they deeply apologized for bringing the sport into disrepute and accepted disqualification and we accept that’s the end of the matter.”

Mathews said organizers are considering new rules for future competitions requiring participants to choose from stones selected by officials instead of finding their own.

The World Stone Skimming Championships does not have any cash prizes, but the winner does receive a trophy.

The first round of the competition features competitors attempting to skip their stones across the surface of the water to the back wall of the quarry, a distance of about 206 feet. Those who qualify for the second round then engage in a “toss off” to determine the winner.

Kentucky man Jonathan Jennings became the competition’s first-ever American winner in the adult male category of this year’s event. Lucy Woods won the adult female category for the sixth time.