There is a hydrogen bomb on the Atlantic ocean floor

In 1958, a 3,400-kg (7,600-pound) hydrogen bomb was lost in the Atlantic ocean. It was carried by a US B-47 bomber when it collided in midair with an F-86 fighter plane. Despite being damaged, the B-47 remained airborne and purposefully jettisoned the bomb into the water to reduce the aircraft weight and prevent the bomb exploding during the emergency landing.

 
Following a number of unsuccessful searches (latest in 2004), the exact location of the bomb remains unknown. While there is little threat of explosion, if not found, sooner or later the bomb will decompose and release the enriched uranium, which will contaminate the surrounding environment with radiation. The bomb sits somewhere in the waters off Tybee Island near Savannah, Georgia, USA.

via wikipedia.org, reddit.com