It is located in the waters of Port Orchard Bay off Brownsville Marina.
Coast Guard boats have established a 1,500-yard safety zone around the device.
It was first discovered floating east of the Marina this afternoon.
Bomb Disposal units are working to safely retrieve the item before it gets any closer to shore.
The Coast Guard is also working to determine how it ended up in the water.
Stay with Action News on air and online as we update this breaking story.