Nen Hithoel is a large lake upon the Great River Anduin amid the Emyn Muil to the east of Rohan. The lake is approximately 20 miles long from north to south, and 10 miles wide. Upon the lake's northern approach from Anduin the Men of Gondor constructed the huge pillars of the Argonath in the reign of Rómendacil II to mark the northern boundary of their realm, although by the time of the War of the Ring that boundary has long since receded. At the southern end of the lake stand three hills. Amon Hen, the "Seat of Seeing", stands upon the western shore and Amon Lhaw, the "Seat of Hearing" upon the east. The third hill forms an island in the lake itself, Tol Brandir. None has ever set foot upon the island due to the intense currents at the lake's south end, for the lake is drained by the falls of Rauros.
The Fellowship of the Ring arrived at Nen Hithoel on February 25, 3019 Third Age, and made camp at Parth Galen close to Amon Hen. The fall of Boromir and the breaking of the Fellowship occurred soon after. Frodo and Sam took a boat for the eastern shore, Merry and Pippin were captured by Orcs, and after sending Boromir's body over the falls in another boat Aragorn, Legolas and Gimli, calling themselves the Three Hunters, set out to track the orcs and find the captive Hobbits.