The Forest River (S. "Taurduin") rose in the Grey Mountains and raced east and south through Mirkwood before feeding into the Long Lake (S. "Annen"), a small but significant body of fresh water lying beyond the eastern edge of the forest. Low hills lined the northern and eastern shores of the Lake, obscuring everything beyond from view except the peak of the Lonely Mountain. (It took about two days to row up the Lake to the Lonely Mountain.)
The Forest River emptied slowly into the Lake. Although it cut through low, stone cliffs – coarse, waterworn, glacial gravel called "shingles" – the widening river picked up only a little speed after virtually stopping in the Long Marshes (S. "Aelinann") between Mirkwood and Long Lake. The Marshes' pools of brackish water and wetland islets seemed to swallow the river after it left the forest.
An eighty-foot waterfall called the Mere's End (S. "Lindal") stood south of Long Lake. The Lakemen of Esgaroth heard these tumbling waters as "a distant roar." Once the site of the Northman town of Londaroth, Mere's End was now only a portage point marked by two great mills.