Esgalduin
From Tolkien Gateway
Esgalduin (S. 'River under veil'; esgal = veil, duin = river) was a major tributary of the Sirion, which rose in the dark heights of the Ered Gorgoroth, and flowed southwestward to meet the Sirion on the western borders of Doriath. It marked the boundary between the forests of Neldoreth and Region.