A river that rose in northern Beleriand not far to the west of Ivrin, where the Narog had its source. The two rivers ran southward, parallel to one another, for about a hundred miles, until the Ginglith's course veered eastward and its waters flowed into the Narog.

South from the point where the Ginglith met the Narog, that larger river became uncrossable, so the Elves of Nargothrond were forced to journey northward to the Ginglith's inflow before they could travel eastward from their realm. This was in the days before the short-lived bridge they built across the Narog, and the Sack of Nargothrond. The final battle of the Elves of Nargothrond was on the plain of Tumhalad, the land that rose between the courses of the Ginglith and the Narog.