Aelin-uial

In The Silmarillion, Aelin-uial, a Sindarin name translated as Meres of Twilight (aelin = lake, uial = twilight), was a marshy confluence of the river Aros into Sirion, south of Doriath.

This area had a strong connection to Ulmo, who was able to send visions to both Finrod and Turgon bidding them to seek a place where a stronghold hidden from the eyes of Morgoth could be established.

Later, when Húrin slew Mîm in the ruins of Nargothrond, he was intercepted in this area by Elves of Doriath and brought before Thingol, bearing the Nauglamír.