Gladden Fields
The Gladden Fields (Sindarin Loeg Ningloron) were a region of wide marshes and reed-beds where the river Gladden flowed into the Anduin, between Lothlórien and the southern eaves of Mirkwood. They were the site of the disaster in which Isildur was slain and the One Ring was lost, and later the place where it was found again.
Geography
The Gladden Fields lay along the eastern side of the Great River, a broad tract of fen and tall reeds named for the golden iris-flowers (gladdens) that grew there. The Gladden stream descended from the Misty Mountains through the Vales of Anduin to join the river amid these marshes.
The Disaster of the Gladden Fields
After the Last Alliance of Elves and Men overthrew Sauron at the end of the Second Age, Isildur, who had cut the One Ring from Sauron's hand and kept it for his own, journeyed north toward his home in the kingdom of Arnor. As his company passed the Gladden Fields, they were ambushed by a host of Orcs. Isildur's guard was overwhelmed and his sons slain. Isildur himself put on the Ring to escape by invisibility, but the Ring betrayed him: it slipped from his finger as he swam the Anduin, and Orc-arrows found and killed him. The Ring sank into the river-bed and was lost for nearly two and a half thousand years.
The finding of the Ring
Long after, it was in the waters near the Gladden Fields that the hobbit Déagol, fishing with his kinsman Sméagol, found the Ring on the river-bottom. Sméagol murdered Déagol for it and became the creature Gollum, beginning the next chapter of the Ring's history.