|Location||Upper vale of the Anduin|
|Description||Short, east-flowing tributary of the Anduin|
The Rhimdath or Rushdown was a short, early tributary of the Anduin River. It flowed from the Misty Mountains eastward into the Anduin roughly halfway between the Langwell-Greylin confluence and the Carrock. Given the name "Rushdown" it probably had a steep gradient.
The stem RIP- means to "rush, fly, fling"; from this comes Quenya rimpa and Noldorin (Sindarin) rhib-, rhimp-, rhimmo, meaning "to flow like a [?torrent]". The stem DAT-, DATH- means "fall down". Christopher Tolkien stated that the name Rhibdath or Rhimdath, meaning "Rushdown" was a hastily scribbled addition at the end of the R-stems. In the index he noted that this name only appeared in the Etymologies but is the river described above.