The River Greyflood (Gwathló) was sourced at the confluence of the Rivers Hoarwell and Glanduin. From there, it flowed to the south-west and emptied into the Great Sea in a gradually widening mouth.

The Greyflood acted as the border between Minhiriath and Enedwaith, and beginning around the year 800 of the Second Age, it was used by the Númenorians to transport lumber harvested fom the immense forests of the two regions.

The Númenorians founded two cities on the Greyflood. At its mouth they built the haven of Lond Daer as both a shipyard and loading area for shipping lumber to the shipyards of Númenor. Where the North-South Road crossed the River they founded Tharbad as a point where logs were shipped downstream to Lond Daer.

Lond Daer was abandoned after the destruction of Númenor but Tharbad survived until the year 2912 of the Third Age, when it was destroyed by the floods that followed the Fell Winter of 2911.
Encyclopedia entry originally written by PotbellyHairyfoot