‘But the Ring was lost. It fell into the Great River, Anduin, and vanished. For Isildur was marching north along the east banks of the River, and near the Gladden Fields he was waylaid by the Orcs of the Mountains, and almost all his folk were slain. He leaped into the waters, but the Ring slipped from his finger as he swam, and then the Orcs saw him and killed him with arrows.’ Gandalf paused. ‘And there in the dark pools amid the Gladden Fields,’ he said, ‘the Ring passed out of knowledge and legend; and evenso much of its history is known now only to a few, and the Council of the Wise could discover no more.'
- The Fellowship of the Ring (Book 1), Chapter
The Gladden Fields are a marshland along the Gladden River, a tributary of the Anduin. At the beginning of the Third Age, Isildur and his three oldest sons were ambushed by Orcs and slain here, resulting in the loss of the One Ring in the marshes' waters.
By the middle of the Third Age, parts of the area were settled by the Stoor hobbits. The Stoor Déagol rediscovered the ring while fishing, only to be killed by his friend Sméagol, who later became known as Gollum. The Stoors have all but deserted the area as servants of Sauron in search of the One Ring now linger here.