Well now....could it be...*ponder*...the River Thales?
No
Is it east of the River Gelion?
Yes
Did something important in the Silmarillion happen at this river?
Yes
Is it one of the rivers of Ossiriand?
Yes
Legolin, perhaps?
No
Do I need soap with that? I really need to clean theses dishes.
I suppose they get cleaner with soap. 
Well, you're coming really close now.
