Huntington Beach, Calif. ? Commercial-grade explosives discovered in a canal south of Los Angeles prompted authorities to ban cell phone use Wednesday to prevent accidental detonation.

Environmental divers hired to check on algae growth found the cigarette-sized blasting caps late Tuesday in a canal lined with homes off of Huntington Beach harbor.

All seven of the volatile explosives, which often are used to trigger larger explosions, were retrieved from the canal, said Jim Amormino, spokesman for the Orange County Sheriff’s Department.

There was no evidence of explosives stronger than the caps, which could cause an explosion equivalent to a hand grenade, Amormino said.