The Lefnui was the westernmost river of southern Gondor.
Course
The Lefnui flowed from its source in the far west of the White Mountains southwest in a partially erratic course through the lands west of the hills of Pinnath Gelin, until it emptied into the Bay of Belfalas through a long narrow firth. It was the longest and broadest of the five rivers Erui, Sirith, Serni, Morthond and Lefnui. The Lefnui formed the western border of Gondor, because the Númenóreans had never established permanent settlements in the promontory of Andrast to its west where they only kept a coast-guard force and beacons at the end of the cape of Andrast.
The Lefnui played little part in history, though it was remembered by the people of Gondor and the Men of Rohan. When the Dunlendings invaded Rohan in T.A. 2758, during the rule of King Helm of Rohan and Steward Beren of Gondor, they were aided by Gondor's enemies from the south, the Corsairs of Umbar. These sea-going marauders landed at Lefnui's mouth on their mission to overrun and destroy the Rohirrim, though they would eventually be defeated.