A small hand grenade dug up in the flower garden of an Amagansett yard was set off last week by Suffolk County police.

According to the county police, a company was installing a sprinkler system at a Stony Hill Road home when a worker hit what he told police he thought was a rock.

After realizing that it might be a hand grenade, he called East Hampton Town Police.

The grenade appeared to be from the World War II era, and Suffolk Police said it appeared to be a live grenade. It was detonated on the spot by the Suffolk police bomb squad, which determined it was too old and fragile to risk moving.

Grenades are discovered from time to time on the East End, said East Hampton Town Police Chief Edward V. Erker Jr.

“We’ve seen them in Montauk because of Camp Hero,” he said, referring to the site of that onetime military base that is now owned by the state. Erker said that about 10 years ago the state began an eradication project to find buried grenades on the property.