Two hand grenades -- one, a practice grenade, the other a smoke grenade -- were found in an area along the shore of Peconic Lake in Calverton on Wednesday night, police said.
Both grenades proved to be live, Suffolk County police said, and have been placed in safe storage awaiting disposal by bomb squad personnel.
The incident, which unfolded in an area along River Road, was reported to Riverhead Town police just before 6:30 p.m. Responding officers secured the area, then contacted the Suffolk Emergency Services Unit, which secured the two grenades for disposal.
It was not clear where the grenades came from.
Police said the incident remains under investigation.