|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.
Rhimdath is derived from the stems RIP- ("rush, fly, fling") and DAT- ("fall down"). Christopher Tolkien stated that the name Rhibdath or Rhimdath, given the 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.