Anduin

The Anduin or Great River is the longest river in J. R. R. Tolkien's fictional Middle-earth (the original Sindarin name means Long River), rising east of the Misty Mountains and flowing south through Wilderland and eastern Gondor. Gondor's ancient capital Osgiliath straddles the river; after the fall of Osgiliath the river effectively marks the eatern limit of Gondor's influence. South of Osgiliath the river turns south west and flows out of a broad delta to the Bay of Belfalas and the Sundering Sea.

It was in the Gladden Fields in the northern reaches of Anduin that Isildur was slain and the One Ring lost; and it was there, more than two millennia later, that Déagol found the ring and Sméagol took it from him.