It is called Lake Nenuial, Sindarin for "Lake of Twilight", by the Elves (Middle-earth), suggesting that it is best seen at that time of day. The lake is about 100 miles north of the Shire in northern Eriador. It is approximately 50 miles from north to south and 20 miles east to west. It is bounded on the west by the Emyn Uial (Hills of Evendim) and on the south by a ridge of hills not named on the map. On its southern shore was Annúminas, the first capital of Arnor.
The Baranduin or Brandywine River flows out of the lake to the east.
wikipedia.org dumped 2003-03-17 with terodump