The Dallas bomb squad was called in to remove a suspicious bag found in the water near the Mountain Creek Parkway bridge on Tuesday.
A Department of Public Safety dive team on routine training in Mountain Creek Lake noticed the bag floating in the water near the bridge. The team opened the bag and found a hand grenade inside.
The team closed the bag, tied it to a buoy and alerted Dallas Fire-Rescue.
The Dallas bomb squad arrived and examined the bag, which also contained wires and bottles. It is not clear if the grenade had a live charge. The bomb squad determined examining the package was not worth the risk to the team member's lives.
The bomb squad detonated it in a safe place just before 5 p.m., police said.
Drivers were not allowed to cross over the bridge while teams removed the bag. The North Texas Tollway Authority reopened the bridge shortly after 6 p.m.
Investigators are working to determine how the bag got under the bridge.
Anyone with information on the case is asked to call Crime Stoppers at 214-373-TIPS (8477). Crime Stoppers is offering up to $5,000 for information that leads to an arrest.