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BOULDER COUNTY, Colo. — Park rangers found a second hand grenade Wednesday after a couple walking around a Boulder County lake accidentally stepped on one Tuesday night, the Boulder County Sheriff’s Office said.

The first device was found Tuesday when Rachel Wine and Anthony Perkins were walking in an area where part of the lake had receded when one of them stepped on the grenade. The two looked at it, realized what it was and called 911.

Wine and Perkins were the only two in the park at the time. The Boulder County Regional Bomb Squad was called in and determined the grenade was live and likely from the World War II era.

Rust had developed over the grenade’s surface from having been at the bottom of the lake for an unknown time, prompting the bomb squad to blow up both grenades. There were no injuries or property damage.

On Wednesday, crews detonated a second grenade that was caked with mud, sand and rust.

Investigators believe the grenades had been buried under the small lake for several years but were recently unearthed because of sinking water levels.

The Boulder County Sheriff’s Office expects the park to remain closed until Friday to allow deputies to search the area to ensure no other devices are still in the area.