Thorn Sir

From Tolkien Gateway

Thorn Sir ("Eagle-stream") was a river according to the early version of the legendarium in The Book of Lost Tales. It was located beneath Cristhorn, at the bottom of a gorge in the Encircling Mountains into which Glorfindel and the balrog fell. After this battle the river was stained black by the balrog's blood for many days.[1] Its Qenya cognate was Eäsindi.[2]

This river was later mentioned as Thornsir in the unfinished Lay of Eärendel,[3] but was not used by J.R.R. Tolkien in any other text.